Discover The Squares Under The Sudoku Fog

** TODAY'S PUZZLE **
A glorious return to the channel tonight for the American math teacher RockyRoer whose puzzle, Square Numbered Fog Totals, teaches us some really weird facts about how square numbers interact with sudoku grids!
Tell your friends about this - it's a genuinely fascinating one!
Play the puzzle at the link below:
sudokupad.app/RJtrMfLmBq
Rules:
Normal sudoku rules apply. Placing correct digits will remove fog from surrounding cells to reveal more clues. Somewhere in the fog are 9 marked cells - one in every row, column and 3x3 box. These cells must contain the digits 1-9 once each. For each marked cell, the sum of ALL the digits in the cells up to and including that marked cell, (top to bottom, left to right, as one might read) must always sum to a square number.
For example, if R4C2 is a marked cell, then the sum of all the digits in row 1, row 2, row 3, R4C1, and R4C2 must be a square number.
** THE LORD OF THE RINGS SUDOKU HUNT RELEASED ON 1 JUNE **
We've just launched the sudoku event of the summer! Blobz' puzzles and Ted Nasmith artistry combined in one of the most beautiful, approachable and fun hunts we've ever published. Get hyped!!! Teaser puzzle here:
sudokupad.app/blobz/a-long-ex...
Play the full version here:
/ crackingthecryptic
Other treats on Patreon include:
- Simon's solve of Sky-Skyscraper by Phistomefel has just been uploaded for our patrons.
- and Mark's latest solve of The Times Club Monthly cryptic crossword
** LAST NIGHT'S BRAID STREAM **
You can watch our stream from last night at this link:
kzbin.infoWcqUhQkwUSY
▶ SUDOKU PAD - Use Our Software For Your Puzzles ◀
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ALSO on Amazon: Search for “SudokuPad”
▶ Contents Of This Video ◀
0:00 Theme music & puzzle intro
2:06 Paws' Sudoku Hunt
2:51 Happy Birthdays
4:32 Rules
5:58 Start of Solve: Let's Get Cracking
▶ Contact Us ◀
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[@rockyroerNPC]

This was a fun surprise. I was literally on the couch trying to make a sequel to this puzzle that only uses the digits 0-8 instead of 1-9, when 3:30 hit and I said, hmmm, I wonder what puzzle Simon's got today. 🙂

[@Jukka70]

well that puzzle was brilliant rockyroer and I hope that you are able to make a sequel using the digits 0 through 8, I think it would be great

[@eclectichoosier5474]

I did your 7x7 the other day. It was great! (I didn't see this one, or I would have tried it.)

[@itztaytay2]

This puzzle was a joy, thank you very much and an 0-8 version sounds quite fun also if you do make it

[@JaymanOttawa]

Such a brilliant puzzle and solve! Really clever...

[@davidrattner9]

Constantly adore how you set and what you come up with!!

[@SirBradiator]

All those 23 pairs could have been resolved a lot earlier by noticing that R3C1 had to be a 3 to make the 10 required for 100

[@kurtu5]

3 plus 7 is teeeeeenennennnnnnn!

[@BramMertens]

Came here to post the same comment. A neurologist with some sort of eye tracker could probably find lots of interesting stuff about how we (or at least Simon) see some details and miss others. Wonderful solve Simon.

[@Mephistahpheles]

@@BramMertens I find the different logical paths that people take are interesting. Simon seems to alternate between "insanely focused" and "completely erratic" with little in between. I'm often left puzzled why he abandons a train of thought......as often as I'm puzzled why he doesn't give up and move on to other stuff. Works for him, though! He's a FAR FAR better solver than I!

[@fakjbf3129]

@@Mephistahpheles Another thing is that he’s also narrating as he goes. He can’t just find something and keep going he has to also think about how to explain it and then do so, which makes everything far harder.

[@Aciek25]

So many Marked cells. Where are Simoned ones?

[@penningmeestercgkdelft9159]

😀

[@HunterJE]

This feels like a useful puzzle to remember that if you know n^2 you can easily get (n+1)^2 by adding 2n+1

[@whaffey313]

I think you mean minus

[@HunterJE]

@@whaffey313 Nope, meant plus. 2^2 + 2 * 2 + 1 = 4 + 5 = 9 = (2 + 1)^2; 5^2 + 2 * 5 + 1 = 25 + 11 = 36 = (5 + 1)^2, try it our with your fave…

[@HunterJE]

Another way to look at it - if you draw a n x n square [area n^2], add n x 1 rectangles along each of two adjacent sides [area 2n], and fill in the missing corner with a 1 x 1 square [area 1], you get a (n + 1) x (n + 1) square [area (n + 1)^2] 🟩🟩🟩🟩🟨 🟧🟧🟧🟧🟩 🟧🟧🟧🟧🟩 🟧🟧🟧🟧🟩 🟧🟧🟧🟧🟩

[@davidgould9431]

​@@whaffey313 But (n + 1)² = n² + 2n + 1, so @HunterJE is right.

[@erikremmelzwaal1225]

Knowing table of squares is very power full when one realize that many n*m can be written as (a+b)(a-b) = a^2 - b^2.

[@vbachris]

i was screaming "3 in R3C1" for half the video because of the 100 sq but i could NEVER solve a puzzle like this. awesome work

[@FryGuy1013]

The "marked cells" thing got me twice in this puzzle. I didn't realize that they would be marked, and thought it was more of a metaphorical marking like when doing doubler puzzles.

[@stevieinselby]

Same here ... to start with I assumed that marked cells were marked and so the whole of the section that was cleared at the start were _not_ marked cells ... then I doubted myself and wondered if it was just cells that we had to mark ourselves ... so knowing roughly where the funky cell in r9 was I zapped 1-2-3-4-5 quickly into r9c8 to see if any markings appeared when it briefly cleared the fog, just so that I could be sure whether or not my initial assumption was correct, without actually paying attention to which digit did clear the fog or which cell the marking appeared in. And then of course like Simon I missed the obvious in r4c3...

[@acantilado]

Same

[@maljamin]

Same. Surprising Simon wouldn't himself find the assumption (of visible marking) peculiar given how many doubler and other modifier cell (plus fog) puzzles he's done. I've never seen a ruleset with cells described as marked with no description of the mark. Let alone with fog!

[@wade_23]

Yeah these rules should have been more clear about that. Tripped me up and I ruined the puzzle too

[@davidgove9327]

@@wade_23 me too!

[@timotab]

41:51 "What on earth am I meant to do with this now?" Sudoku, Simon, the answer is always sudoku. With that given 8.

[@Ferrastar]

You can’t ask Simon to do Sudoku in a Sudoku puzzle

[@xerodeus2337]

marking the 9 at 32:30 could have been figured out awhile ago, because he knew in those 3 boxes was definitely a 9, and definitely a marked square. The marked square could never be the 3rd cell (R3C3) because it would mean 9 plus 2 cells would add up to 10!

[@samuelraustein187]

hahah classic Simon. Misses the easy stuff

[@Daymickey]

I was looking for this comment wondering if I was wrong or something 😂

[@BramMertens]

Feature request for your software: some sort of "notes" or tips field for each cell so you could keep track of things like these squares and sums. Amazing how you were able to keep track without something like that.

[@Tsunami14]

Funny. I was about to suggest the exact same thing.

[@georgen4246]

Simon: As the numbers get bigger, the gaps between squares gets bigger. Simon: Let's continue from the small end. 😆

[@jensschmidt]

Ignoring Sudoku on R2C4 for weeks (at least it felt like weeks) is such a Simon thing to do....

[@hilburn-]

The 3 in R3C1 was so stressful, can't believe it was basically the last digit!

[@phballer99]

! sometimes find these kinds of notes (especially the ones with the "simple" logic explanations that are paragraphs long lol) a bit overkill. That said, this one I absolutely agree with. 😂

[@alphazero924]

Simon is incredibly brilliant, but the way his brain has to seemingly fully switch from sudoku to another ruleset in order for him to see things like that can be frustrating as a viewer. Still love the videos though.

[@Timlagor]

I'm such a sucker for a fog puzzle

[@Glamador]

I was so baffled at the start. I'm so used to having to make the marks myself that I didn't think that the cells might be pre-marked and we could assume the ones we see at the start aren't.

[@jonotick]

This was a classic case of me getting stuck, scrolling through Simons solve to get to the point where i am stuck - feel quite proud it was 30ish minutes into his solve - and wait for the "oh good grief this is beautiful" to see where he made the breakthrough and then go back and find the breakthrough for myself knowing i was on the right track but just needed Simon's confirmation!

[@lordatog]

I think I need a rules clarification before I can start this. What makes a cell "marked"? Are they clearly visibly different in some way (and therefore there are none in the 9 cells visible at the start)? Are they not visibly different, and their locations must be deduced? Are they the cells that begin prefilled, making the initial 9 a marked cell? All 3 of these seem like possible options.

[@trudain]

40 mins. But wrote out a table of squares and options where they could go on paper. No way I could keep straight in my head otherwise. Also got stuck. Watched the video a bit that reminded me a rule I forgot so could continue.

[@Arcessitor]

Same on both counts. I didn't realize the fog revealed the things around the 9 weren't marked. (Cause usually you do it yourself).

[@Jukka70]

That puzzle was incredible, one of favorites in ages, and I do love seeing them all, but this was special. I was hooked from beginning to end and able to follow the logic all the way through.

[@olanmills64]

The next time there is a similar rule like this, I hope it is made more clear that marked squares actually have graphical markings built in to the puzzle set up. Because there have been other puzzles where the same term was used, but you are meant to discover and do the marking yourself. I was banging my head trying to make progress, so I decided I needed help and started skimming through Simon's solve, and I was like, "Hang on, how does Simon know that none of the nine initially revealed squares are not marked squares?" I didn't realize those could be eliminated as possible marked squares. But otherwise, this was a really cool, interesting rule set

[@Dojak1981]

at 19:25 we could have concluded that r3c3 is green, couldn't we? (I haven't watched the video to the end yet) we know that either r3c2 or r3c3 is 9, so if r3c3 would be red it would mean that we would need to get 10 worth of digits in 3 cells including a 9.

[@RichSmith77]

Yes, *we* can. (Just not Simon, on this occasion).

[@Sam_on_YouTube]

Puzzles like this, with such a simple rule set and so few clues are really clever. It took me a while to realize that none of the square cells could be in the exposed part and that was a very important part of the break-in. But by the time I realized that, I had so much marked up that it unlocked the puzzle leading to a smooth solve from there.

[@user-cb3qr9dt2k]

I love your channel, Following your mind is a treat. Many times I have to pause to find how you got there by logic, but thats why I love it.

[@RealCadde]

19:23 I mean, isn't it obvious that if R3C3 is a marked square and you are going for a hundred. You'd have 90 in two rows, then you'd definitely have a 9 in that row of box one for a sum of 99. You would have to put a 1 and a 0 with a 9 for a total of 100 if R3C3 was a marked square. Zero is not a valid Sudoku digit.

[@MattYDdraig]

25:27 Beautiful idea and great execution. The maths side made placing the marked cells reasonably easy, but still left a lot of work to clear up. I particularly liked that the first three marked cell digits placed were 169, a square number.

[@lcpholman]

50:14 - ha ha - finally! That 54 pair's been hiding in plain sight for so long :)

[@emilywilliams3237]

Fascinating. I always love your videos, Simon - thank you for this one. Not too mathsy, as you said the sudoku itself forces many things!

[@davidrattner9]

Like your word of Mathsy. 🙂

[@emilywilliams3237]

@@davidrattner9 Ah, I can take no credit for that - it was Simon's word!

[@erickehr4475]

24:18 for me. What I found quite unusual about this fog of war puzzle was that the next deduction wasn’t always in a part of the grid near to the previous deduction.

[@stevieinselby]

True - the disjoint set across the funky cells was an interesting way to ping the solve around to different parts of the grid.

[@dinane]

I loved this. Good math practice :) and even interesting sudoku at the end. This was fun!!!

[@MarcyProbably]

Managed to get this in under an hour, I'm quite please with myself. Beautiful puzzle!

[@StaceyGreenstein]

My first thought: Since there needs to be a marked cell in c9, then that sum must be both square and divisible by 45. The only possibility less than or equal to 405 (9*45) would be 225, which is 5x45=15^2, so r5c9 must be marked.

[@TheKtuno]

Too much maths for me to even attempt this one but once again my mind is blown that RockyRoer is brilliant and creative enough to set such a unique puzzle! Astounding!

[@karnowo]

Been waiting to see the solve of this. Attempted it when it came out and it's been doing my head in.

[@EmmaSolomano]

I rarely take notes for sudokus, but I’ll admit I got out the spreadsheet for this one. I noted all the possible square numbers, which row the relevant marketed cell would appear in, and the totals in the row that each one must add up to (subtracting the sums of the previous rows). I marked all the possibilities in the grid then whittled them down based on the sudoku rules. Then I had the positions of all the marked cells. Then got stuck shortly after that 😂 luckily Simon is always there to lend a hand and help me get the next step in the logic that I have missed.

[@brock2k1]

Was the assumption that the cells were literally marked warranted? There have been many FOW puzzles with one "special" cell per box where they were not marked, and the Japanese squares puzzle a few days ago actually said that hidden cells were colored when they were not.

[@RichSmith77]

They haven't been described as "marked cells" in other puzzles where we've had doublers, pseudo cells and the like to find. If it's described as a marked cell, I thought it was clear the cell would be marked in some way. (Not sure which the Japanese squares puzzle was - what was the video called?)

[@brock2k1]

@@RichSmith77 Thanks for the response. I'm very sorry --- not only did I mistakenly write "Japanese Squares" instead of "Japanese Sums," I mistakenly thought the puzzle was just a few days old. It was actually a year old, but I only solved it a few days ago when I googled for Fog of War puzzles. The puzzle was "Go the Right Way" by Pantera, but the title of the CtC video was "Which Way in the Fog?" and Mark did the solve. Sorry I can't give an exact date; KZbin just says 1 year ago. If you search for "shade" in the comments of that puzzle, you will see that several people were confused by the rules implying that both the clue cells and the target cells are blue shaded, when in fact only the clues are shaded.

[@RichSmith77]

@@brock2k1 I found that Japanese Sums puzzle that incorporated fog that you referenced. I agree, the rules for that particular puzzle were a little ambiguous. (I even found an old comment from myself in a thread back then, that was discussing whether two adjacent shades clue cells always had to be read as a double digit number, or could they be two single digit clues that happened to be adjacent.) I agree that those rules could have been read as suggesting some cells in the 6x6 were already shaded, and would be revealed by removing fog. I'd probably put it down to that being a particularly complicated rule set that the constructor had attempted to make as concise as possible, and didn't realise by doing so, they had introduced some ambiguities. Especially for people unfamiliar with Japanese Sums puzzles, which the constructor was very familiar with. I think that was more a failing of that particular puzzle, though. I can see how recent experience of that puzzle might make you wary of the wording of this puzzle, but I still think it would be a failure of the wording in this puzzle (like with the Japanese Sums puzzle) if marked cells didn't have some marking visible once the fog was cleared.

[@EmmaSolomano]

I rarely take notes for sudokus, but I’ll admit I got out the spreadsheet for this one. I noted all the possible square numbers, which row the relevant market cell would appear in, and the totals in the row that each one must add up to (subtracting the sums of the previous rows). I marked all the possibilities in the grid then whittled them down based on the sudoku rules. Then I had the positions of all the marked cells. Then got stuck shortly after that 😂 luckily Simon is always there to lend a hand and help me get the next step in the logic that I have missed.

[@frankjiang1857]

Finished in 32:47. For those who are stuck with the break-in, 1st the cells are MARKED which means that the cells don't have something in it special, then it is NOT marked. Second map out where the squares of each row can be. Also, for later in the puzzle, try to do some sudoku to clear out the entire fog, because there are some clues hidden in the fog that without them it would be impossible to solve (as I tried to do for a good 10 minutes :p solving). Fun puzzle!

[@alanclarke4646]

Not seeing it. Won't bother to try the puzzle.

[@TheDecagn]

I discovered the fact later, very helpful to know that marked cells actually exist (would be more clear if we started with a marked cell or something) thank you!

[@DarkChasm]

Yeah very cool concept, liked it alot, not too diff but till cracking a little bit. ❤❤❤❤

[@Lottie842]

Puzzles like this make me realize I’ll never be truly brilliant at sudoku because I’m not that good at math. 😂 In other words, Simon, your math skills blow my mind.

[@Tepalus]

Had like 2h... Next time I will read the instructions more carefuly lol "mark some cells" and "there are marked cells" is a HUGE difference😅

[@eclectichoosier5474]

There was a very similar new Rocky Roer puzzle on LMD just the other day. Lots of fun. One thing about Rocky Roer - you know that when you see that name, you're gonna have a good time!

[@sarvagyatiwari6585]

This was such a clever puzzle, absolutely loved it!

[@ericpraline1302]

I happened to do this on LMD a couple of weeks ago. It's a beautiful idea executed brilliantly. RR seems to one of the most inventive setters out there.

[@dekomali]

Great puzzle! Right down my alley.

[@G0LD3N_12]

i was screaming behind my screen for the 3 in R3C1 😂😂

[@chocolateboy300]

I finished in 149 minutes. This was such a unique and fun ruleset. I must be tired, because I messed up on my math several times. I put a 78 pair in row 2, instead of 68. I thought that row 7 was 29, instead of 19. That cost me so much time. I enjoyed this one, though. Great Puzzle!

[@enchanter1520]

I really wished that sudoku wouldn't disambiguate those 2-3 pairs and Simon would've had to use the marked cell at row 3. We knew that R3C1 + R3C2 add up to 10. That gives a 3 since we have 7 in the marked square. Great solve nonetheless.

[@johnh2052]

A key moment should have occurred at 18:00 when Simon was examining box 1. R3C3 cannot be a marked cell because the total would be over 100. The marked cell is R3C2. This is critical a little later when examining boxes 4 and 7 because it means that there is an x-wing on marked cells, and the marked cell in column 1 will be a 9 regardless of which box it occurs in. And _this_ gives you the location of the 9 in box 1.

[@TheNewAccount2008]

Awesome puzzle, really nice. Took me 45 minutes, which I did not expect given the length of Simons video...

[@kibels894]

Wow that's a cool puzzle, it even has roping somehow?

[@tianyi05]

At 42:43 the 7 in R3C2 gave the 3 in R3C1 which resolved alot of the 23 pairs earlier.

[@sakkikoyumikishi]

19:08: "... and that could be just about anything." Nooooo! I mean, *yes,* but NO, you were so close! Yes, it can be (almost) any digit, but we actually know one thing it is for sure, and that is a marked digit! Think about it like this: We have two positions that the 9 can go in in box 4. Wherever it goes, the first either two or three cells of row 3 need to sum up to 10. So if it goes in r3c2, that implies that r3c1 is a 1, true, because otherwise we would overshoot the 10 goal. But it ALSO implies that r3c2 has to be a marked digit, since we couldn't possibly add a third digit to our two cells that already sum to 10 and make the result still sum to 10. The only other option is that the 9 could be in r3c3, in which case it would AGAIN imply that r3c2 has to be the marked digit. Because if r3c3 were the marked digit and contained a 9, then we would again have to make three cells that contain a 9 sum to 10 (or, in other words, make two cells sum to 1), which is obviously impossible. So while we might not know what DIGIT r3c2 contains, we can say with certainty that it has to be the marked digit of box 1

[@davidrattner9]

Cherish your enthusiasm Simon when you solve fog and if reveals itself!!

[@guilded0n3]

Squell the best combination for square and cell that he constantly wants to say.

[@Xiuhtec]

Took me just over an hour, like 30 minutes of which was just trying to work out and remember the differences of multiples of 45 and squares in my head as I lie in bed on my phone and can't take written notes or anything.

[@adamdobrowolski2510]

I finished in 32m7s. The easiest way IMO is to write out the potential squares up to 405, with color coding by row. They are some givens, like c5r5 and c1rX, but the rest rely on surprisingly approachable deductions. I think it's definitely a sub-30 puzzle if you get a warm up from a similar puzzle; I needed some time to do the pencil marking AND THEN some time to watch up to the concept.

[@RichSmith77]

The first thing I did was put the multiples of 45 in the cells in the final column (45,90,135,etc). I then put the squares into the first cells of each appropriate row for that square. So 49, 64, 81 in r2 c1-3; 100, 121 in r3 c1-2; etc. I then realised I was only actually interested in how much above the multiple of 45 at the end of the previous row, each square was. So I converted my squares to mod 45 values, and had these pencil-marked into the first few cells of each row. For instance, once you know the square in row 6 is 256, all you really need to remember/pencil-mark is that this is 31 (mod 45). So just put 31 at the start of row 6.

[@jasonmetcalfe4695]

Totally awesome puzzle idea I loved it

[@RoderickEtheria]

I wasn't sure we could necessarily rule out the 3×3 square visible to us. It's not told to us what a marked square would look like if it were revealed.

[@coconuts2513]

Somewhere in the fog are 9 marked cells...

[@RoderickEtheria]

A lamppost illuminating fog doesn't mean the fog stops existing.

[@RichSmith77]

​@@RoderickEtheriaIt's part of the fog mechanic though. The fog is cleared revealing given digits, clues, grid markings and the like beneath. If there are marked cells in the grid, I'd expect them to be visible once the fog had been removed from the cell.

[@RoderickEtheria]

@@RichSmith77 The fog is still there. It's just been revealed.

[@RichSmith77]

@@RoderickEtheria I think it's just a Simonism to say the fog has been revealed. The rules clearly state the fog is removed if a correct digit is entered. I've always assumed Simon means to say the grid has been revealed whenever he says the fog has been revealed. It would be preferable if he didn't say the fog has been revealed, but he's been saying it for so long now, I'm not sure we can ever break his habit.

[@benjaminrealy5661]

40:54. I had no difficulty in placing the marked squares. Then drew cages to the nearest sides when there was only 1 possible square total. I forgot to draw one simple one summing to 10 in box 1 and it slowed me down when i couldnt proceed. Twas a great relieving aha moment. 11/10. Possibly the best solve ive ever done that i enjoyed. Love maths puzzles

[@mostman]

This was a joy to solve.

[@SarahLivne]

Arrrrgh! It wasn't at all clear to me that the "marked" cells would be visibly marked clues on the grid (as opposed to special cells I'd have to mark myself). I was stuck for hours till I turned back to the video, still did not understand Simon's assumption, then saw it in the comments and SMHed. Would have been so much clearer if the rules actually stated HOW the cells were marked, making it clear from the start that the 9 cells that were initially clear of fog could not contain any "marked" cell. Otherwise - a very cool puzzle.

[@markp7262]

29:09 finish. I'm glad that I listened to Simon go over the rules after I read them, because I would have had a lot of trouble adding things up to prime numbers. Don't even ask me how I got that. Always love the math puzzles though. Excellent!

[@RichSmith77]

You're the second person I've seen mention prime numbers. Did I miss something, or do you also mean square numbers, not primes?

[@markp7262]

@@RichSmith77 I meant that when I read the rules, for some reason I read prime numbers instead of squares. Which would have made the puzzle a LOT harder to solve.

[@RichSmith77]

@@markp7262 Ah, I see what you mean. 🙂 Sorry.

[@markp7262]

@@RichSmith77 No worries. I didn't explain it well enough before. Apparently I'm having trouble reading AND talking. 🤣🤣🤣

[@Ziltoid23]

Had a go myself and got stuck at the point you reach around 35 minutes. I also did not manage to spot that r4c3 was indeed not marked! Back to the puzzle..

[@Ziltoid23]

Update: did it! Took ages to spot the requirement for a 9 to be to the right of the marked square in row 6

[@AcanthaRayneOakMoon]

When I first read the rules, I thought it was going to have the same mechanic reading vertically too. It took me an embarrassingly long time to realise that wasn't the case.

[@memy02]

would love to see a little text pad that can be added to the sides of the puzzle so you can type notes that are not on top of the puzzle

[@MarkWiseTechno]

62:53 for me on this one. Super unique concept with logic that I would call tough but fair. Nice puzzle!

[@Kinada]

70 minutes. Felt I was being a bit slow there too. Really interesting puzzle.

[@chrisbaeyens4513]

Magical that this exists! A nice qol feature would be if you could add notes to cells (excel style). Sven?

[@titusadduxas]

1:41:47 - Wow! - Amazing construction which I found very difficult! I could have done with a scratch pad.

[@mikepictor]

I....did it. I normally don't even bother with puzzles that took this long, but I decided I could just wrrite down all the possible squares, and then I wouldn't have to keep thinking them up, and then....I actually did it. ~48 minutes...not bad.

[@FrancisFjordCupola]

50:20 "Oh, the five and the four are resolved." said Simon. Which happened about four minutes earlier when he wrote the 5 into box nine. I'm still convinced Simon just does that to make us feel smart. Look at me! I can spot something a genius can't until much later! Or perhaps the cracking is just such a load on the brains the room for scanning goes down way low. I just find that fascinating. I wonder how often that sort of thing happens in IT; when people fail to spot a simple solution because they have worked so hard on their logic skills they lose sight of the less complex. It does have a relation to societal issues.... :P

[@piarittersporn]

Brilliant puzzle.

[@Mega_Tron6891]

I love math and even my brain was struggling to keep up with all the numbers, but that may be the Friday nightcap slowing me down😂😂

[@Yttria]

Found this one challenging up to finding the I-wing on 9's in box 5 (finally found it after pencil marking the grid and was afraid I'd have to find a y-wing to continue). Also missed the row 7 logic requiring 1 to be part of the 19. Finished in 66:01 with the row 7 nudge help from the video.

[@chipsounder4633]

Fascinating find again.. who would have thought this could be possible to build as not only a sudoku, but a fog of war sudoku... how lol 😮🎉

[@bait6652]

Is the Makes u wonder 2 things )1) How many solutions are there w/o the given 2) what other sequences can be done w the marked ruleset. And can't wait for the next design using 2 marked cells per.

[@MarkLudwick]

I loved this one

[@jasonbourne7047]

It was fun to see how long it took Simon to get R2C4 as 6 due to the black digit 8 in R8C4 😂

[@apiyo_puzzles]

Wow! If the next best of book can handle a fog of war, this should be in it!

[@nidhiagrawal7878]

If you can share that possible options are as below(in the rules), the puzzle starts much more easily (for people who do not remember the squares) 45 4, 9, 16, 25, 36 90 49, 64, 81 135 100, 121 180 144, 169 225 196, 225 270 256 315 289 360 324 405 361, 400

[@sacredsock8031]

3 rules for doing sudoku: 1. Remember to do the sudoku 2. If in doubt, look at where the cursor is 3. Nope, that pretty much covers it

[@RichSmith77]

Did anyone else approach it like I did? The first thing I did was pencilmark the multiples of 45 in the cells in the final column (45,90,135,etc). I then put the squares into the first cells of each appropriate row for that square. So 49, 64, 81 in r2 c1-3; 100, 121 in r3 c1-2; etc. I then realised I was only actually interested in how much above the multiple of 45 at the end of the previous row, each square was. So I converted my squares to mod 45 values, and had these pencil-marked into the first few cells of each row. For instance, once you know the square in row 6 is 256, all you really need to remember/pencil-mark is that this is 31 (mod 45). So just put 31 at the start of row 6. I wasn't any faster than Simon, but I was close to his time, which I'm not normally.

[@estherwestbroek]

I did, though instead of mod 45 I wrote down heads and tails eg 19 / 26 or 9/36 and on notepad instead of in the puzzle.

[@James-qz8iy]

9:00 The sum of the first n rows is 45n = n * 5 * 3^2. For this to be square each power in the above factorisation must be even. So n = 5.

[@JohnRandomness105]

Rather interesting that Simon placed the 3 in R3C1 during the last few Sudoku digits, rather than summing to ten.

[@slomopanic]

Near the end R3c1 was a forced 3 since you needed 10 for the square number to be correct :D

[@LednacekZ]

24:15 those squares at the start are laborious, the rest is easy.

[@KrisCadwell]

Nice solve.

[@xerodeus2337]

I got the opening and then realized this was going to be too much math for my brain :D

[@Sam_on_YouTube]

Finished in 39:39. I definitely needed to flip between the calculator and the browser on my phone.

[@RealCadde]

38:20 I think this is one of the few times i am going to forgive Simon for not doing sudoku using the given 8 in R8C4. But only because he has no option to make comments in the grid. The given 8 sees R2C4 and makes it a 6. But Simon used to have a 6/4 notated there for the eight-squared number. Simon simply "can't trust" his pencil marks now. And would have done well to get rid of all "comments" he made beforehand. I also want to suggest that the software provides a means of commenting on cells in a different color like yellow and is simply a string. And letting you type a whole novel if you want, but it would show the first N characters and reduce font size the way center pencil marks do. If a novel is written, simply hovering over the comment text will show the full contents as a tag.

[@davidjesus1397]

Am I missing something or how could r3c3 ever be marked once you know that there a 9 in r3 box1? Then you would have 3 numbers, including one 9, adding up to 10

[@TheDarkNerd]

I only got the puzzle to the state Simon had it at around 36:20 before getting absolutely stuck. I'm not great at figuring out larger potential combinations without a calculator similar to the one in the Killer Sudoku app >.>

[@MaxPower2719]

15:07 “Let’s put a box around it.”

[@srwapo]

My timer said 105:25, but I think I forgot to pause for like 20-30 minutes at some point. I did take a LOT of notes on what could be used to make square numbers for every row (yes, on a spreadsheet), still took a lot of work from there. And seeing some given digits that I kept ignoring.

[@markthompson2874]

Screaming at Simon that the bottom 3 rows are striping!

[@markthompson2874]

Oops, I mean roping! He figured it out eventually, sometimes a lot easier to find things watching than actually doing it.

[@johnhumberstone9674]

I'm a bit confused here. What is revealed when the fog clears?

[@RichSmith77]

Sometimes given digits are revealed. It always reveals whether a cell is one of the marked cells or not.

[@carljacobs1287]

Oddly enough. I think this puzzle would have worked almost as well without the fog. The fog however forces you to think in a way that aids the solving of this puzzle.

[@RichSmith77]

Without the fog, you lose 80% of what the puzzle is all about, deducing where the marked cells go.

[@johnh2052]

I can't believe the 3 in box 1 was nearly the last digit filled in. :) Well, I _can_ believe it, of course.

[@CaptainSpock1701]

25:30 - "It's very odd this..." Given that it is squares, I'd say it is very even though!

[@sakkikoyumikishi]

33:22: "So we've found, well... We've approximately found the red 9." Nope, you had it right the first time. r4c3 is no longer in the fog, revealing that it *isn't* a marked digit. By extension, the two remaining marked digits have to be r4c1 and r8c3. And that tells us that the red 9 specifically is in r4c1.

[@Pointlesschan]

He finally saw it but man, it bugged me that he missed it for so long

[@Kirbyfan87827]

Finished in 41:42 with help from the video.