Problem #21

Problem link
Solution:

package main

import (
    "math"
)

func main() {
    sum, j := 0, 0
    for i := 1; i < 10000; i++ {
        j = sumOfProperDivisors(i)
        if i == sumOfProperDivisors(j) && i != j {
            sum += i
        }
    }
    println(sum)
}

func sumOfProperDivisors(input int) int {
    //checking until the square root is enough
    //since a divisor less than the square root corresponds
    //the other divisor greater than the square root
    limit, sum := int(math.Sqrt(float64(input))), 0
    for i := 1; i <= limit; i++ {
        if input%i == 0 {
            if i == input/i {
                sum += i
            } else {
                sum += i + (input / i)
            }
        }
    }
    return sum - input
}

Result: 31626
Time: 0m0.023s