给定一个正整数a，找到最小的正整数b，它的每个数字相乘之后等于a

0,3=>0,5=>0,7=>0];

    foreach ($facts as $fact=>$num) {
        while ($input%$fact ==0) {
            $input = $input/$fact;
            $facts[$fact]++;

            //已经分解到最底层了，结束遍历
            if (isset($facts[$input])) {
                $facts[$input]++;
                break 2;
            }
        }
    }

    //最后无法被个位数的质数分解，就是没有答案
    if (!isset($facts[$input])) {
        return 0;
    }
    if ($facts[3]>1) {
        $facts[9] = intval($facts[3]/2);
        $facts[3] = $facts[3]%2;
    }
    if ($facts[2]>2) {
        $facts[8] = intval($facts[2]/3);
        $facts[2] = $facts[2]%3;
    }
    if ($facts[2]>1) {
        $facts[4] = intval($facts[2]/2);
        $facts[2] = $facts[2]%2;
    }
    if ($facts[2]==1 && $facts[3]==1) {
        $facts[2]=$facts[3]=0;
        $facts[6] = 1;
    }
    ksort($facts);
    $str = '';
    foreach ($facts as $fact=>$num) {
        $str .=str_repeat(strval($fact), $num);
    }
    return intval($str);
}

$param = $argv;
$input = intval($param[1]);
var_dump(factorization($input));