gmp_nextprime

(PHP 5 >= 5.2.0)

gmp_nextprimeFind next prime number

Description

resource gmp_nextprime ( int $a )

Find next prime number

Parameters

a

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

Return the next prime number greater than a, as a GMP number.

Examples

Example #1 gmp_nextprime() example

<?php
$prime1 
gmp_nextprime(10); // next prime number greater than 10
$prime2 gmp_nextprime(-1000); // next prime number greater than -1000

echo gmp_strval($prime1) . "\n";
echo 
gmp_strval($prime2) . "\n";
?>

The above example will output:

11
-997

Notes

Note:

This function uses a probabilistic algorithm to identify primes and chances to get a composite number are extremely small.

Коментарии

Автор:
It seems gmp_nextprime on negative numbers always returns 2.
2016-02-09 19:21:04
http://php5.kiev.ua/manual/ru/function.gmp-nextprime.html
Prime numbers are positive, non-zero numbers that have exactly two factors. No more, no less. So testing negative numbers doesn't really make any sense.
2016-06-08 19:17:12
http://php5.kiev.ua/manual/ru/function.gmp-nextprime.html
Negative numbers N always have at least four factors: N*1=N and abs(N)*-1=N. Therefore, even if "natural number" weren't in the definition of a prime (which it is), no negative number would ever qualify. Therefore, the next-largest prime number to any negative number is always 2.
2017-02-03 06:01:51
http://php5.kiev.ua/manual/ru/function.gmp-nextprime.html

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