PHP Manual: Check if number is "probably prime"

Description

int gmp_prob_prime(GMPintstring $num, int $repetitions = 10)

The function uses Miller-Rabin's probabilistic test to check if a number is a prime.

Parameters

num

The number being checked as a prime.

A GMP object, an int or a numeric string.

repetitions

Reasonable values of repetitions vary from 5 to 10 (default being 10); a higher value lowers the probability for a non-prime to pass as a "probable" prime.

A GMP object, an int or a numeric string.

Return Values

If this function returns 0, num is definitely not prime. If it returns 1, then num is "probably" prime. If it returns 2, then num is surely prime.

Examples

Example #1 gmp_prob_prime example

<?php
// definitely not a prime
echo gmp_prob_prime("6") . "\n";

// probably a prime
echo gmp_prob_prime("1111111111111111111") . "\n";

// definitely a prime
echo gmp_prob_prime("11") . "\n";
?>

The above example will output:

0
1
2