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.
Contents
Famous Primes
Fermat Primes
Mersenne 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.
