Erlang solution to the cube permutation problem

percubes.erl

% permcubes.erl
%
% Problem statement:
% The cube, 41063625 (345^3), can be permuted to produce two other cubes: 56623104 (384^3) and 66430125 (405^3).
% In fact, 41063625 is the smallest cube which has exactly three permutations of its digits which are also cube.
% Find the smallest cube for which exactly five permutations of its digits are cube.
%
% Usage: permcubes:find(N) where N is the number of permutations
% permcubes:find(N). =>  [127035954683,352045367981,373559126408,569310543872, 589323567104]

-module(permcubes).
-export([find/1]).
-export([is_permutation/2]).
-export([get_permutations/2]).

% returns the list of N cubed numbers that are permutations
find(N) -> find(1, N, []).
find(X, N, L) ->
    Cube = trunc(math:pow(X, 3)),
    Permutations = get_permutations(L, Cube),
    Count = length(Permutations),
    if (Count < N-1) ->
        find(X+1, N, L ++ [Cube]);
    true ->
        Permutations ++ [Cube]
    end.


% true is N and M are string permutations of each other
is_permutation(N, M) ->
    ListN = integer_to_list(N),
    ListM = integer_to_list(M),
    lists:sort(ListN) == lists:sort(ListM).

% returns a list of permutations of N from L
get_permutations(L, N) -> get_permutations(L, [], N).
get_permutations([], R, N) -> R;
get_permutations(L, R, N) ->
    [M|L2] = L,
    Isperm = is_permutation(M, N),
    if (Isperm) ->
        get_permutations(L2, R ++ [M], N);
    true ->
        get_permutations(L2, R, N)
    end.