C++ Count Factors
long long countFactors(long long n)
{
    long long count = 0;
    long long 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.