Euler3.exs

# largest factor of 600851475143

defmodule Problem3 do

# http://wende.github.io/2015/09/07/Elixir-n-prime-numbers.html

  def prime?(x), do: (2..round(:math.sqrt(x)) |> Enum.filter(fn a -> rem(x, a) == 0 end) |> length()) == 0

  def solve(num) do
    (2 .. round(:math.sqrt(num)))
    |> Stream.filter(&(rem(num, &1) == 0))
    |> Stream.filter(&(prime?(&1)))
    |> Enum.to_list
  end
  
  def print do
    IO.inspect solve(600851475143)
  end

end

Problem3.print