A prime number is a whole number larger than the number 1 that can be divided evenly *only* by itself and 1. The first and smallest prime number is the number 2. It’s the only even prime number. All primes after 2 are odd because all even numbers can be divided evenly by 1, themselves, and 2, and so don’t fit the definition of a prime number.

When you recognize that a number is prime, you don’t waste time trying to find things to divide into it when you’re reducing a fraction or factoring an expression. There are so many primes that you can’t memorize or recognize them all, but just knowing or memorizing the primes smaller than 100 is a big help. Here they 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, 97