perms.erl

-module(perms).
-export([perms/1]).

% Calculate the Permutations of a list
perms([]) -> [[]];
perms(L)  -> [[H|T] || H <- L, T <- perms(L--[H])].

sieve.erl

-module(sieve).
-export([primes/1]).

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

count(X) ->
  count(X,[]).

count(X,L) when X >= 2 ->
  count(X - 1,[X | L]);
count(X,L) when X < 2 ->
  L.

% Find primes less than X using the Sieve of Eratosthenes
primes(X) ->
  sieve(count(X)).