prac2.ex

defmodule Prac2 do
  def prime?(2) do true end
  def prime?(n) when n < 2 do false end
  def prime?(n) when rem(n, 2) == 0 do false end
  def prime?(n) do check(3, n) end

  defp check(a, b) do
    if a * a <= b do
      if rem(b, a) == 0 do
        false
      else
        check(a + 2, b)
      end
    else
      true
    end
  end
end

# 1..100 |> Enum.filter(&(Prac2.prime?/1))