6, 8, 10, 14 and 15.
For a number to have [only] 2 factors, it must be a prime number; the prime numbers between 0 and 20 are; 2, 3, 5, 7, 11, 13, 17, 19
There is an infinite number of numbers between 0 and 20.
2,3,5,7,11,13,17,19
There are 9 prime numbers between 0 and 20: 1,2,3,5,7,11,13,17,19.
The prime numbers between 0 and 20 are: 2, 3, 5, 7, 11, 13, 17 and 19
There are 19 numbers between zero and 365 that have an odd number of factors.
2, 3, 5, 7, 11, 13, 17, and 19 each have two factors . . . '1' and itself.
2,3,5,7,11,13,17,19
Eight of them.
All of the odd numbers in that range can be factors.
50
20