I use factor trees:
450
/ \
50 9
/ \ / \
10 2 3 3
/ \
5 2
(You stop at the prime numbers because otherwise you could have infinite 1s and the prime factorization wouldn't be unique.)
when you are finished the factor tree you take the last values and they are the prime factors.
The prime factorization of 450 is 22335 or 2²3²5
Hope this helps :)
