function convert_to_base62($n)
{
        $base = 62;
        $str = "";

        while ($n != 0)
        {
            $r = $n % $base;
            $n = (int)($n / $base);

            if($r >= 10 && $r <= 35)
            {
                $str .= chr(87 + $r );
            }

            else if($r >= 36 && $r <= 61)
            {
                $str .= chr(29 + $r);
            }

            else
            {
                $str .= (string)$r;
            }
        }

        return strrev($str);
}