## What is a prime number?

A **prime number** (or a **prime**) is a natural number that is greater then 1 and that has no positive divisors other then the number 1 and itself. For example, 7 is prime, because 7 can only be divided by 1 and itself. The fundamental theorem of arithmetic establishes the central role of primes in number theory: any integer greater than 1 is either a prime itself or can be expressed as a product of primes that is unique up to ordering. Prime numbers are very popular in modern encryption methods. The higher a prime number is, the more secure the encryption is since the factorization takes a very long time.