Go Count Factors
func countFactors(n int) int {
	count := 0
	i := 1
	for 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.