Wouldn't it be fun if someone out there already knows a simple way to determine if a number is prime without factoring, but to them it is so obvious that they didn't even consider others may be interested.
That’s fine for GIMPS, which only searches for Mersenne primes, but doesn’t work in general.
https://en.wikipedia.org/wiki/Primality_test#Fast_determinis... mentions several tests that do not require factorization, though.
Fermat Reincarnation. > Fermat Reincarnation.