arctan = x - x * x * x / "3" + x * x * x * x * x / "5" - x * x * x * x * x * x * x / "7" + x * x * x * x * x * x * x * x * x / "9" - x * x * x * x * x * x * x * x * x * x * x / "11" + x * x * x * x * x * x * x * x * x * x * x * x * x / "13" - x * x * x * x * x * x * x * x * x * x * x * x * x * x * x / "15" + x * x * x * x * x * x * x * x * x * x * x * x * x * x * x * x * x / "17" - x * x * x * x * x * x * x * x * x * x * x * x * x * x * x * x * x * x * x / "19" + x * x * x * x * x * x * x * x * x * x * x * x * x * x * x * x * x * x * x * x * x / "21" - x * x * x * x * x * x * x * x * x * x * x * x * x * x * x * x * x * x * x * x * x * x * x / "23";