65
None of them.
All of them.
No number under 100 has 13 factors. 60, 72, 84, 90, and 96 each have 12 factors.
30 is the only number between 20 and 50 that is a factor of 60
No numbers in that range have an odd number of factors.
56
52 has 6 factors.
Every one of them has an even number of factors.
If it has an odd number of factors (greater than 3) then it must be a perfect square that is not the square of a prime number. This leaves 42, 62, 82 and 92. The answer is 82 = 64 which has the factors 64, 32, 16, 8, 4, 2 and 1.
66
13/60 is in its simplest form as there are no common factors for 13 and 60
60, 72, 84, 90 and 96 each have twelve factors.