Question

How many ways two integers can be written as product of two distinct numbers?

Answer 1

For example, for 36=22⋅32, we have 3⋅3=9 "total" divisors (1,2,3,4,6,9,12,18,36) but 5 ways to express 36 as a product of two factors (36⋅1,18⋅2,12⋅3,9⋅4,6⋅6). So if the question talks about two "different" factors, you have to subtract 1 and divide to 2 (in this example we have to exclude the product 6⋅6). Sep 17, 2016