function commonPrimeDivisors(array $a, array $b): int
{
    $gcd = static function (int $n, int $m) use (&$gcd) {
        if ($n % $m === 0) {
            return $m;
        }

        return $gcd($m, $n % $m);
    };

    $removeCommonPrimeDivisors = static function (int $n, int $m) use ($gcd) {
        while ($n !== 1) {
            $d = $gcd($n, $m);
            if ($d === 1) {
                break;
            }
            $n /= $d;
        }

        return $n;
    };

    $counter = 0;
    for ($i = 0, $count = count($a); $i < $count; $i++) {
        $x = $a[$i];
        $y = $b[$i];
        $d = $gcd($x, $y);

        $x = $removeCommonPrimeDivisors($x, $d);
        if ($x !== 1) {
            continue;
        }

        $y = $removeCommonPrimeDivisors($y, $d);
        if ($y === 1) {
            $counter++;
        }
    }

    return $counter;
}