Try looking at a few numbers, finding all of their factors, and seeing what patterns you can find.
For instance, the number 8 has factor pairs of 1 and 8, and 2 and 4. This is four factors.
The number 9 has factor pairs of 1 and 9, and 3 and 3. Since "3" is listed twice, this is actually only three factors.
The number 10 has factor pairs of 1 and 10, and 2 and 5: four factors.
The number 11, being prime, has only the pair 1 and 11: two factors. (So
any prime will have just the two factors, and now you know not to bother with primes.)
The number 12 has factor pairs 1 and 12, 2 and 6, and 3 and 4: six factors.
The number 16 has factor pairs 1 and 16, 2 and 8, and 4 and 4. Since "4" is occurs twice, this is actually only five factors.
Notice that we always had an even number of factors, unless the number was a square, so that one of the pairs was actually the same factor twice. What does this suggest...?