Definition: prime number

An integer greater than 1 that is not evenly divisible by any number other than itself, and, of course, 1. Prime numbers are considered a fundamental building block of numbers, especially number theory, a branch of mathematics.

The first 10 prime numbers are 2, 3, 5, 7, 11, 13, 17, 19, 23 and 29. Except for 2, all primes are odd numbers. As the numbers get higher, prime numbers tend to be found in pairs that are close together; for example, 29,669 and 29,671 are primes. The largest prime number thus far, which contains more than 65,000 digits, was discovered in 1986.