Tinyurl-style unique code: potential algorithm to prevent collisions

Question

I have a system that requires a unique 6-digit code to represent an object, and I\'m trying to think of a good algorithm for generating them. Here are the pre-reqs:

Answer 1

Any prime number which is not a factor of the length of the sequence should be able to span the sequence without repeating. For 64000000, that means you shouldn't use 2 or 5. Of course, if you don't want them to be generated consecutively, generating them 2 or 5 apart is probably also not very good. I personally like the number 73973!