Formula Needed for a Programming Issue?

I have two sets of variable combinations and I need a formula to find a result.

Knowns:

Number of items in A=2

Number if items in B=3

Total combinations: A*B = 6

If Item A values are 1 and 2

and Item B values are 1, 2 and 3

What formula would give me a range of 1-6 (total combinations)

Example Set

A B Result

1 1 =1

1 2 =2

1 3 =3

2 1 =4

2 2 =5

2 3 =6

The proof of the formula would be to have A=3 and B=4 where you end up with a new total combination of 3*4=12

The formula will be used in a programming application to resolve passed in values of A and B and use them to lookup a values in the result array (1-6).

Thanks in advance for all your help with this puzzle.