Mapping two integers to one, in a unique and deterministic way

Question

Imagine two positive integers A and B. I want to combine these two into a single integer C.

There can be no other integers D and E which combine to C. So combining

Answer 1

Let number a be the first, b the second. Let p be the a+1-th prime number, q be the b+1-th prime number

Then, the result is pq, if a or 2pq if a>b. If a=b, let it be p^2.