MathPHP\Probability\Combinatorics::lahNumber PHP Метод

    public static function lahNumber(int $n, int $k)
    {
        if ($n < 1 || $k < 1) {
            throw new Exception\OutOfBoundsException("n and k must be < 1 for Lah Numbers");
        }
        if ($n < $k) {
            throw new Exception\OutOfBoundsException("n must be >= k for Lah Numbers");
        }
        $nCk = self::combinations($n - 1, $k - 1);
        $n！ = self::factorial($n);
        $k！ = self::factorial($k);
        return $nCk * ($n！ / $k！);
    }