defmodule AmicableNumbers do
  def divisors(n) do
    [ 1 |
    (for i <- 2..floor(:math.sqrt(n))//1,
      div(n, i) == n / i do
        [i, div(n, i)]
    end |> Enum.flat_map(&(&1))) ]
  end
end

ns = for i <- 1..10_000, into: %{} do
  {i, AmicableNumbers.divisors(i) |> Enum.sum()}
end

for {a, b} <- ns,
  a != b,
  ns[b] == a,
  reduce: 0 
do
  acc -> a + acc
end
|> IO.puts()