def check(2) , do: true

   def check(n) when n >2 do

        b = for x <- (Enum.into 2..n-1,[]),do: x

        if chec(n,b,[]) == [] do

          true

        end

   end

    def chec(n,[m|r],ss) when rem(n,m) ==0, do: chec(n,r,[m|ss])

    def chec(n,[m|r],ss), do: chec(n,r,ss)

    def chec(n,[],ss), do: ss

  def span2(n) when n > 2 do

     for x <- (Enum.into 2..n, []), check(x) == true , do: x

  end

  def span2(n), do: "n must > 2"

IO.inspect(span2(40))

[2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37]