anchor.diff:  -export([factorial/1]).
   -export([pandigital/1]).
   -export([palindrome/1]).
  +-export([factors/1]).
   
   primes(N) ->
     L = lists:seq(2, N),
  
positive.code:   sets:from_list(S) == sets:from_list(lists:seq($1, $0 + length(S))).
  
  palindrome(N) ->
    lists:reverse(integer_to_list(N)) == integer_to_list(N).
negative.code: is_prime(N, I) when N rem I == 0 -> false;
  is_prime(N, I) -> is_prime(N, I + 2).
  
  factors(N) -> factors(N, 2).
  factors(N, _I) when N =< 1 -> [];
  factors(N, I) when N rem I == 0 -> [ I | factors(N div I, I) ];
  factors(N, I) -> factors(N, I + 1).
  
  divisors(N) ->
    [ A || A <- lists:seq(1, N div 2), N rem A == 0].
  