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Primality Test

Tool to check if a number is a prime number. A primality test is a mathematical and algorithmic test that indicates whether a number is prime or compound and answers true or false.

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Primality Test -

Tag(s) : Arithmetics, Mathematics

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# Primality Test

## Prime Number Tester

Tool to check if a number is a prime number. A primality test is a mathematical and algorithmic test that indicates whether a number is prime or compound and answers true or false.

### How to know if a number is a prime?

To know if a number is prime, it need to check if it has any divisor except 1 or itself, this test is called a primality test.

Example: Is 23456789 a prime number ? True

Example: Is 123456789 a prime number ? False

### What are primality tests algorithms?

It exists several test to know if a number is a prime number : Miller–Rabin or Lucas-Lehmer are the one used by dCode.

### What is the prime numbers test algorithm?

The algorithm tries all or almost all numbers (it avoids even numbers and multiples of 3). Here is a pseudo code applicable for prime numbers not too large:  function is_prime(n) { if n ≤ 1 return FALSE else if n ≤ 3 return TRUE else if (n mod 2 = 0) or (n mod 3 = 0) return FALSE i = 5 while (i*i ≤ n) { if (n mod i = 0) or (n mod (i + 2) = 0) return FALSE i = i + 6 } return TRUE