started challenge 3 with erlang

e3/e3.erl

@@ -0,0 +1,18 @@
+-module(e3).
+-export([e3/0, factor/3]).
+
+% e3 get largest prime factor
+
+% returns list of prime factors
+factor(N, Factors, Divisor) when N == 1; Divisor >= N-1 -> %io:format("done ~p/~p\n", [N, Divisor]), 
+  [N]++Factors;
+factor(N, Factors, Divisor) when N rem Divisor == 0 -> %io:format("match ~p/~p\n", [N, Divisor]), 
+  Factors++factor(Divisor, [], 2) ++ factor(trunc(N/Divisor), [], 2);
+factor(N, Factors, Divisor) -> %{io:format("inc ~p/~p\n", [N, Divisor]),}%
+  factor(N, Factors, Divisor+1).
+
+max([], Max) -> Max;
+max([H|T], Max) when H > Max -> max(T, H);
+max([H|T], Max) -> max(T, Max).
+
+e3() -> max(factor(600851475143, [], 2), 0).