A prime number is a number with exactly two positive factors: itself and 1. It's very helpful to be able to recognize the prime numbers between 1 and 100. There are 25 of them, and they are as follows:
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97.
If you like pictures, then the following chart may help you remember which numbers are prime and which are not. The prime numbers are colored blue:
REMEMBER: 1 is neither prime nor composite!