Prime number

A prime number (or simply prime) is a positive integer whose only positive divisors are 1 and itself. Note that is usually defined as being neither prime nor composite because it is its only factor among the natural numbers.

Famous Primes

Twin Primes

Two primes that differ by exactly 2 are known as twin primes. The following are the smallest examples:
3, 5
5, 7
11, 13
17, 19
29, 31
41, 43

Advanced Definition

When the need arises to include negative divisors, a prime is defined as an integer p whose only divisors are 1, -1, p, and -p.