# Prime Number Checker

Factorising Calculator / Prime Number Checker
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Enter a natural number to be factorised.

Enter a number and the Prime Number Checker will instantly tell you if it is a prime number or not.

The calculator will also find all of the factors of the number.

## What is a prime number?

A prime number is a number whose only divisors are 1 and itself.

Let us quote some prime numbers: 7, 11, 13, 17, 19,… and some larger ones: 22 091, 9 576 890 767

## How check if a number is prime?

A natural number (greater than or equal to 2) is a prime number if it has exactly two divisors: 1 and itself. Just try to divide it by the prime numbers less than its square root.

## Example: Is 107 a prime number?

- we calculate the square root of 107, it is approximately equal to 10.3.

- we try to divide 107 by the prime numbers less than or equal to 10 i.e. 2 3 5 7

- one carries out the division of 107 successively by 2,3,5 and 7.

- 107 is not divisible by these numbers, therefore it is prime.

## Can negative numbers be prime?

No, because a negative number has at least four divisors in Z. The number −a then has as divisors: 1, −1, a and −a.