input: def exponential_series(x: float, n: int) -> float:
      """ Calculate the sum of an exponential series from 0 to n, given a base x.
      >>> exponential_series(2, 3)
      15.0
      >>> exponential_series(3, 2)
      13.0
      """
      sum = 0
      for i in range(n+1):
          sum += x ** i
      return sum
output:     sum = 0
      for i in range(n+1):
          sum += x ** i
      return sum