A natural number is called PRIME when it is greater than 1, only divisible by 1 and by itself.

For example: 5 is a prime number because its divisors are only 1 and 5.

On the contrary 6 isn't a prime number because its divisors are not only 1 and 6, but also 2 and 3.

PROPERTIES

Prime numbers are countless: this was demonstrated by mathematicians such as Euclid and Euler.

An old method for finding prime numbers is the sieve of Eratosthenes

Prime numbers are the basis for all the integer numbers, as it is stated by the fundamental theorem of the arithmetic:

“Every natural number greater than 1 accepts a unique factorization in prime numbers and the order of factors is irrelevant”