Quote by Mathguy15
I have heard of a construction that gives a set of integers that cannot be factorized uniquely. Consider the numbers that have an even number of distinct primes as factors. It is not hard to see that the primes of this set are those integers that have at most two distinct prime factors. Let p and q be two ordinary prime numbers. Then, p^2*q^2=(pq)^2. Since p^2, q^2, and pq have no factors in this set, p^2*q^2 is a counterexample to unique factorization in this set. I suspect that something similar may happen when an even number is replaced with multiples of any integer. Maybe something like this is what you were looking for? You might be looking for something a great deal more advanced. This is just what I've heard that might be related to what you want.

SORRY, I did not carefully read your post. You are looking for something specifically about the REU. Sorry for my redundant ramblings.
edit:Sorry for the repost.