Factorization algorithm

The algorithm for factoring a number n as I've implemented it goes something like the following.

• Trial division. Using a precomputed number of primes (currently all those less than 1 million), test if any divide n. If so, add them as factors, divide n by them, and continue.

• See if n is a perfect power (in which case its factors are easy to get). Details here: https://github.com/dkhofer/primes/wiki/Finding-perfect-powers

• See if Pollard's Rho algorithm turns up any factors: https://github.com/dkhofer/primes/wiki/Pollard's-Rho-algorithm

• Brute force

In the future, I plan to add in one or more number sieve algorithms.