1 files changed, 26 insertions, 0 deletions
diff --git a/problem21.erl b/problem21.erl
new file mode 100644
index 0000000..1661801
--- /dev/null
+++ b/problem21.erl
@@ -0,0 +1,26 @@
+-module(problem21).
+-export([solve/0]).
+
+solve() ->
+	L = test(1, []),
+	pairs(L, 0).
+
+test(10000, L) ->
+	L;
+test(A,L) ->
+	D = [X || X <- lists:seq(1, erlang:trunc(math:sqrt(A))), (A rem X) =:= 0],
+	E = [A div Y || Y <- D],
+	F = sets:to_list(sets:from_list((D ++ E) -- [A])),
+	G = lists:sum(F),
+	test(A+1, [{A,G}|L]).
+
+pairs([_], S) ->
+	S;
+pairs([{A,B}|T], S) ->
+	M = lists:member({B, A}, T),
+	if
+		M ->
+			pairs(T, S+A+B);
+		true ->
+			pairs(T, S)
+	end.