%% Problem %% --------------------- %% The arithmetic sequence, 1487, 4817, 8147, in which each of the terms %% increases by 3330, is unusual in two ways: (i) each of the three terms %% are prime, and, (ii) each of the 4-digit numbers are permutations of one another. %% %% There are no arithmetic sequences made up of three 1-, 2-, or 3-digit %% primes, exhibiting this property, but there is one other 4-digit increasing sequence. %% %% What 12-digit number do you form by concatenating the three terms in this sequence? %% --------------------- -module(p049). -export([solve/0]). -include_lib("eunit/include/eunit.hrl"). solve() -> Primes = [ X || X <- mymath:primes_upto(9999), 1000 < X ], [ {N, M+N, 2*M+N} || N <- Primes, M <- lists:seq(1,8999), lists:member(M+N, Primes), permutated(N, M+N), lists:member(2*M+N, Primes), permutated(N, 2*M+N) ]. permutated(N, M) -> lists:sort(integer_to_list(N)) == lists:sort(integer_to_list(M)). permutated_test() -> ?assertEqual(true, permutated(1487, 4817)).