What is the worlds most long math problem?

Answer 1

There is no longest problem. Some problems are very easy to state but require a very long proof. Some are easy to prove )or evaluate) but the answer is very long.

An example of the first is that there is no solution to xn + yn = zn for positive integers x, y and z when n is an integer greater than 2.

On the other hand the ratio, pi = circumference/diameter of a circle has been know for thousands of years. But the exact value of pi cannot be written in any base (other than pi or directly related) is infinitely long.