Count Factors

PHP Count Factors

function countFactors(int $n): int
{
    $count = 0;
    $i     = 1;
    while ($i * $i < $n) {
        if ($n % $i === 0) {
            $count += 2;
        }
        $i++;
    }
    if ($i * $i === $n) {
        ++$count;
    }

    return $count;
}

This checks divisors in pairs up to the square root, which keeps the work much smaller than testing every number.