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GMP Functions
PHP Manual

# gmp_prob_prime

(PHP 4 >= 4.0.4, PHP 5)

gmp_prob_prime — Check if number is "probably prime"

### Description

int gmp_prob_prime ( resource `$a` [, int `$reps` = 10 ] )

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

### Parameters

`a`

  The number being checked as a prime.

  It can be either a GMP number resource, or a numeric string given that it is possible to convert the latter to a number.

`reps`

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

  It can be either a GMP number resource, or a numeric string given that it is possible to convert the latter to a number.

### Return Values

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

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GMP Functions
PHP Manual