Finding divisors is often hard when your number is large. It turns out the condition that a number n can be expressed as a multiple of two other numbers is equi

Finding divisors is often hard when your number is large. It turns out the condition that a number n can be expressed as a multiple of two other numbers is equivalent to there being a number z less than n except for 1 and n-1 so that (z^2 mod n) == 1. This condition is the basis of the Miller-Rabin primality test. Sadly its a bit hard for humans to implement this algorithm for mentally proving primality.