21: amicable numbers

21_amicable_numbers/main.go

@@ -0,0 +1,34 @@
+package main
+
+import "fmt"
+
+func main() {
+	var nums []int
+	sum := 0
+	for i := 1; i < 10000; i++ {
+		if isAmicableNumber(i) {
+			nums = append(nums, i)
+			sum += i
+		}
+	}
+	fmt.Println("sum:", sum, "nums:", nums)
+}
+
+func sumOfDivisors(input int) int {
+	sum := 0
+	for i := 1; i <= input/2; i++ {
+		if input%i == 0 {
+			sum += i
+		}
+	}
+	return sum
+}
+
+func isAmicableNumber(input int) bool {
+	da := sumOfDivisors(input)
+	db := sumOfDivisors(da)
+	if da == db {
+		return false
+	}
+	return input == db
+}