Elixir - Problems Solving - Prime number

prime.exs

defmodule Prime do
  @moduledoc """
    A number 'n' is prime only when it is not divisible by any number between 2 and √n
  """
  def run(2), do: true
  def run(num) when num > 2 and rem(num, 2) != 0 do
    is_prime(3, num, round(:math.sqrt(num) + 1))
  end
  def run(_), do: false

  defp is_prime(start, _, stop) when start >= stop, do: true
  defp is_prime(start, num, stop) do
    if rem(num, start) == 0, do: false, else: is_prime(start + 2, num, stop)
  end
end

IO.gets("Enter the number: ")
|> String.strip
|> String.to_integer
|> Prime.run
|> case do
  true -> IO.puts "Prime number"
  false -> IO.puts "Not prime number"
end