PHP Factorial calculation usng BC Math extension

bcmath_factorial

<?php

define('F_NUMBER', 25);

function factorial($in) {
    // 0! = 1! = 1
    $out = '1';

    // Only if $in is >= 2
    for ($i = 2; $i <= $in; $i++) {
        $out = bcmul($out, (string)$i);
    }

    return $out;
}

echo factorial(F_NUMBER);