diff --git a/cmd/21/main.go b/cmd/21/main.go
new file mode 100644
index 0000000..f144b34
--- /dev/null
+++ b/cmd/21/main.go
@@ -0,0 +1,61 @@
+package main
+
+import (
+	"fmt"
+	"math"
+)
+
+const maxLen = 10000
+
+func main() {
+	divList := make([]int, maxLen)
+	numList := make([]int, 0, 100)
+	for i := 0; i < maxLen; i+=1 {
+		if divList[i] > 0 {
+			continue
+		}
+		sum := sumDiv(findDiv(i))
+		divList[i] = sum
+
+		if sum >= maxLen {
+			continue
+		}
+
+		if divList[sum] == 0 {
+			divList[sum] = sumDiv(findDiv(sum))
+		}
+
+		if divList[sum] == i && sum != i {
+			numList = append(numList, i, sum)
+		}
+	}
+
+	fmt.Printf("List: %v\n", numList)
+	fmt.Printf("Sum: %d\n", sumDiv(numList))
+}
+
+func findDiv(num int) []int {
+	out := []int{1}
+	minDiv2 := num
+	for i := 2; i < int(math.Sqrt(float64(num))); i+=1 {
+		if i == minDiv2 {
+			break
+		}
+		if num % i == 0 {
+			div2 := num / i
+			out = append(out, i, div2)
+			minDiv2 = div2
+		}
+	}
+
+	return out
+}
+
+func sumDiv(list []int) int {
+	sum := 0
+	for _, i := range list {
+		sum += i
+	}
+
+	return sum
+}