diff --git a/problems/21/solution.ex b/problems/21/solution.exs
similarity index 80%
rename from problems/21/solution.ex
rename to problems/21/solution.exs
index 80781ae..4770dee 100644
--- a/problems/21/solution.ex
+++ b/problems/21/solution.exs
@@ -2,8 +2,9 @@ defmodule AmicableNumbers do
   def divisors(n) do
     [ 1 |
     (for i <- 2..floor(:math.sqrt(n))//1,
-      div(n, i) == n / i do
-        [i, div(n, i)]
+      j = div(n, i),
+      j == n / i do
+        if i !== j, do: [i,j], else: [i]
     end |> Enum.flat_map(&(&1))) ]
   end
 end