[xcombelle]

if you know the number is a factorial for example

    9! = 9 × 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1

you have are half way of having prime factorization, you can just to compute the prime factor from 1 to 9

and you get

   9! = 3^2 x 2^3 x 7 x 3 x 2 x 5 x 2^2 x 3 x 2 x1