defmodule Grains do
  @doc """
  Calculate two to the power of the input minus one.
  """
  @spec square(pos_integer()) :: {:ok, pos_integer()} | {:error, String.t()}
  def square(number) when number > 64 or number < 1, do: {:error, "The requested square must be between 1 and 64 (inclusive)"}
  def square(number), do: {:ok, 2 ** (number - 1)}

  @doc """
  Adds square of each number from 1 to 64.
  """
  @spec total :: {:ok, pos_integer()}
  def total, do: {:ok, 2 ** 64 - 1}
end