What is the 'Collatz Conjecture' that even the best mathematicians cannot solve?

What is the 'Collatz Conjecture' that even the best mathematicians cannot solve?
According to this assumption, put forward by Lothar Collatz in the 1930s, any number chosen will always increase to 1 using two rules, Here, two rules need to be applied, starting with any positive number, If the number is even, it is divided by two; if it is odd, it is multiplied by three and 1 is added, The process is repeated with the resulting number. Until it reaches 1