Hello I was just wondering if anyone could help me find a conjecture, theorem, hypothesis around this particular result.

If p,q are prime numbers, m,n are integers, and f(r) is the number of nontrivial divisors of r (ie. not 1 or r itself).

That if r=(p^m)*(q^n) (p≠q) that f(r)=(m+1)n+(m-1)

Thanks, I just really suck at looking for previous groundwork involving this.