diff --git a/05_smallest_multiple/main.go b/05_smallest_multiple/main.go
index 0c879a9..ac9aba6 100644
--- a/05_smallest_multiple/main.go
+++ b/05_smallest_multiple/main.go
@@ -5,7 +5,7 @@ import "fmt"
 func main() {
 	n := 20
 	for {
-		if IsDivisibleFor1to20(n) {
+		if IsDivisible(1, 20, n) {
 			fmt.Println("evenly divisible by all of the numbers from 1 to 20:", n)
 			return
 		}
@@ -13,8 +13,8 @@ func main() {
 	}
 }
 
-func IsDivisibleFor1to20(n int) bool {
-	for i := 1; i <= 20; i++ {
+func IsDivisible(start, end, n int) bool {
+	for i := start; i <= end; i++ {
 		if n%i != 0 {
 			return false
 		}
diff --git a/05_smallest_multiple/smallest_multiple_test.go b/05_smallest_multiple/smallest_multiple_test.go
index 6547c99..bff37d4 100644
--- a/05_smallest_multiple/smallest_multiple_test.go
+++ b/05_smallest_multiple/smallest_multiple_test.go
@@ -2,19 +2,39 @@ package main
 
 import "testing"
 
-func TestIsDivisibleFor1to20(t *testing.T) {
+func Test_isDivisible(t *testing.T) {
 	tt := []struct {
 		name  string
+		start int
+		end   int
 		input int
 		want  bool
 	}{
+		{
+			"2",
+			1,
+			2,
+			2,
+			true,
+		},
+		{
+			"10",
+			1,
+			10,
+			2520,
+			true,
+		},
 		{
 			"20",
+			1,
+			20,
 			20,
 			false,
 		},
 		{
 			"14",
+			1,
+			20,
 			14,
 			false,
 		},
@@ -22,9 +42,9 @@ func TestIsDivisibleFor1to20(t *testing.T) {
 
 	for _, tc := range tt {
 		t.Run(tc.name, func(t *testing.T) {
-			got := IsDivisibleFor1to20(tc.input)
+			got := IsDivisible(tc.start, tc.end, tc.input)
 			if got != tc.want {
-				t.Errorf("IsDivisibleFor1to20(%d)=%v, want %v", tc.input, got, tc.want)
+				t.Errorf("IsDivisible(%d)=%v, want %v", tc.input, got, tc.want)
 			}
 		})
 	}
diff --git a/23_non_abundant_sums/abundant_test.go b/23_non_abundant_sums/abundant_test.go
new file mode 100644
index 0000000..a3668d3
--- /dev/null
+++ b/23_non_abundant_sums/abundant_test.go
@@ -0,0 +1,82 @@
+package main
+
+import (
+	"reflect"
+	"testing"
+)
+
+func Test_isAbundantNumber(t *testing.T) {
+	tt := []struct {
+		name  string
+		input int
+		want  bool
+	}{
+		{
+			"1",
+			1,
+			false,
+		},
+		{
+			"12",
+			12,
+			true,
+		},
+		{
+			"28",
+			28,
+			false,
+		},
+	}
+
+	for _, tc := range tt {
+		t.Run(tc.name, func(t *testing.T) {
+			got := isAbundantNumber(tc.input)
+			if got != tc.want {
+				t.Errorf("isAbundantNumber() = %v, want %v", got, tc.want)
+			}
+		})
+	}
+}
+
+func Test_sumOfDivisors(t *testing.T) {
+	tt := []struct {
+		name  string
+		input int
+		want  int
+	}{
+		{
+			"1",
+			1,
+			0,
+		},
+		{
+			"2",
+			2,
+			1,
+		},
+		{
+			"4",
+			4,
+			3,
+		},
+		{
+			"12",
+			12,
+			16,
+		},
+		{
+			"28",
+			28,
+			28,
+		},
+	}
+
+	for _, tc := range tt {
+		t.Run(tc.name, func(t *testing.T) {
+			got := sumOfDivisors(tc.input)
+			if !reflect.DeepEqual(got, tc.want) {
+				t.Errorf("sumOfDivisors() = %d, want %d", got, tc.want)
+			}
+		})
+	}
+}
diff --git a/23_non_abundant_sums/main.go b/23_non_abundant_sums/main.go
new file mode 100644
index 0000000..1fdbd37
--- /dev/null
+++ b/23_non_abundant_sums/main.go
@@ -0,0 +1,55 @@
+package main
+
+import "fmt"
+
+func main() {
+	sum := 0
+	var nums []int
+	ans := make(map[int]struct{})
+	for i := 1; i < 28123; i++ {
+		if isAbundantNumber(i) {
+			ans[i] = struct{}{}
+		}
+		find := false
+		for k := range ans {
+			d := i - k
+			if d < 0 {
+				break
+			}
+			if _, f := ans[d]; f {
+				fmt.Printf("%d = %d + %d\n", i, k, d)
+				find = true
+				break
+			}
+		}
+		if !find {
+			sum += i
+			nums = append(nums, i)
+		}
+	}
+	fmt.Println("abundant numbers:", ans)
+	fmt.Println("sum:", sum, "nums:", nums)
+}
+
+func isAbundantNumber(input int) bool {
+	return sumOfDivisors(input) > input
+}
+
+func sumOfDivisors(input int) int {
+	if input < 2 {
+		return 0
+	}
+	sum := 0
+	i := 1
+	for i*i <= input {
+		if input%i == 0 {
+			sum += i
+			j := input / i
+			if j != i && j != input {
+				sum += j
+			}
+		}
+		i++
+	}
+	return sum
+}