Starting an erlang branch, starting with #001

e001.erl

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+% Add all the natural numbers below one thousand that are multiples of 3 or 5.
+
+% If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.
+% Find the sum of all the multiples of 3 or 5 below 1000.
+
+-module(e001).
+-export([
+    main/1
+    ]).
+
+sum(3) ->
+    0;
+sum(Max) ->
+    N = Max - 1,
+    if
+        N rem 3 == 0 ->
+            A = N;
+        N rem 5 == 0 ->
+            A = N;
+        true ->
+            A = 0
+    end,
+    sum(N) + A.
+
+main(_) ->
+    io:format("Sum of <   10: ~w~n", [sum(10)]),
+    io:format("Sum of < 1000: ~w~n", [sum(1000)]).