Any integer factors, more or less uniquely, into prime numbers. Does this question make sense for real numbers? What about numbers of the form a+b*i where i^2=-1 and a,b are integers? What about numbers of the form a+b*root(N) where a,b,N are integers?
(Possible appendix: What does this concept have to do with Fermat's Last theorem, and what does FLT say anyway?)
