The answers are 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, and 97.
All of these number CANNOT be divided by any number (or cannot have any smaller numbers multiplied together to make it) besides 1 and itself (1 * 5 = 5).