PHP: gmp_nextprime - Manual (original) (raw)

(PHP 5 >= 5.2.0, PHP 7, PHP 8)

gmp_nextprime — Find next prime number

Description

Parameters

num

A GMP object, an int, or a string that can be interpreted as a number following the same logic as if the string was used in gmp_init() with automatic base detection (i.e. when base is equal to 0).

Return Values

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

Examples

Example #1 gmp_nextprime() example

<?php $prime1 = gmp_nextprime(10); // next prime number greater than 10 <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>p</mi><mi>r</mi><mi>i</mi><mi>m</mi><mi>e</mi><mn>2</mn><mo>=</mo><mi>g</mi><mi>m</mi><msub><mi>p</mi><mi>n</mi></msub><mi>e</mi><mi>x</mi><mi>t</mi><mi>p</mi><mi>r</mi><mi>i</mi><mi>m</mi><mi>e</mi><mo stretchy="false">(</mo><mo>−</mo><mn>1000</mn><mo stretchy="false">)</mo><mo separator="true">;</mo><mi mathvariant="normal">/</mi><mi mathvariant="normal">/</mi><mi>n</mi><mi>e</mi><mi>x</mi><mi>t</mi><mi>p</mi><mi>r</mi><mi>i</mi><mi>m</mi><mi>e</mi><mi>n</mi><mi>u</mi><mi>m</mi><mi>b</mi><mi>e</mi><mi>r</mi><mi>g</mi><mi>r</mi><mi>e</mi><mi>a</mi><mi>t</mi><mi>e</mi><mi>r</mi><mi>t</mi><mi>h</mi><mi>a</mi><mi>n</mi><mo>−</mo><mn>1000</mn><mi>e</mi><mi>c</mi><mi>h</mi><mi>o</mi><mi>g</mi><mi>m</mi><msub><mi>p</mi><mi>s</mi></msub><mi>t</mi><mi>r</mi><mi>v</mi><mi>a</mi><mi>l</mi><mo stretchy="false">(</mo></mrow><annotation encoding="application/x-tex">prime2 = gmp_nextprime(-1000); // next prime number greater than -1000echo gmp_strval(</annotation></semantics></math>prime2=gmpnextprime(−1000);//nextprimenumbergreaterthan−1000echogmpstrval(prime1) . "\n"; echo gmp_strval($prime2) . "\n"; ?>

The above example will output:

Notes

Note:

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

Found A Problem?

Tommy Lynge Jrgensen ¶

9 years ago

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.

IceMetalPunk at gmail dot com ¶

8 years ago

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.

Anonymous ¶

9 years ago

It seems gmp_nextprime on negative numbers always returns 2.