public static function randomNumber($prefix = '4', $length = 8)
    {
        if (function_exists('random_int')) {
            $length = $length - strlen($prefix);
            $result = $prefix;
            while ($length > 0) {
                $result .= static::randomNumberUsingRandomInt('', $length > 9 ? 9 : $length);
                $length -= 9;
            }
            return $result;
        }
        $key = "";
        $pattern = '1234567890';
        for ($i = 0; $i < $length - strlen($prefix); $i++)
        {
            $key .= $pattern[mt_rand(0, 9)];
        }
        return $prefix . $key;
    }