Erlang - Goldbach's conjecture - http://en.wikipedia.org/wiki/Goldbach%27s_conjecture

goldbach.erl

%Demonstrates the Goldbach's conjecture - Every even integer greater than 2 can be expressed as the sum of two primes
%
% author: Bruno Jessen
%

-module(goldbach).

-export([primes/1, goldbach/1]).

 

%get all the primes using the classical sieve of eratosthenes

primes(N) -> 

      sieve([], lists:seq(2, N)).

sieve(P, [H|T]) -> 

      sieve(P ++ [H], [X || X <- T, X rem H /= 0]);

sieve(P, []) -> P.

 

 

goldbach(N) when N < 3 ; N rem 2 =/= 0 ->

    [not_a_valid_goldbach_number];

goldbach(N) ->

    Primes = primes(N),

    goldbach(N, Primes, []).

    

 

goldbach(_, [], Acc) ->

    Acc;

goldbach(N, L, Acc) ->

    [H|T] = L,

    R = N - H,

%    io:format("H = ~p, T = ~p => member of ~p:~p ~n",[H, R, L, lists:member(R, L)]),

    NewAcc = lists:append(Acc, [{H,R} || lists:member(R, L)] ),

    goldbach(N, T, NewAcc).