primes.ex

defmodule Prime do
  def prime_factors(number) do
    first_divisor =
      div(number, 2)..1
      |> Enum.find(&(rem(number, &1) == 0))

    case first_divisor do
      1 -> [number]
      _ -> prime_factors(div(number, first_divisor)) ++ prime_factors(first_divisor)
    end
    |> Enum.uniq
  end
end

input = hd(System.argv)
number = String.strip(input) |> String.to_integer
IO.puts "Prime factors of #{number} are #{inspect Prime.prime_factors(number)}"