Distinct products in 2 ranges.

/sci/ needs more mathsematics.

For any n, m positive integers, consider the sets N = {x positive integer | x < n} and M defined likewise. How many distinct products are there of one element of N and one of M?

Let K = (M-1)(N-1).
The answer is K - (# of primes < K)

http://www.youtube.com/user/Horsecockluver