Factoring large numbers is a difficult problem in general. The particular number you cite is small enough to be fairly easy. &Math::Pari::factor doesn't take much time to find that the prime factors of 133745531 are 467 and 286393. You may also have a system program called 'factor' which will give that result somewhat more slowly.

The difficulty of this problem is the basis of RSA public key cryptosystems.

After Compline,
Zaxo