input: Write a function to calculate an exponential series. The function should take two parameters, `x` and `n`, and return the sum of the series from `x^0` to `x^n`.
  assert exponential_series(2, 3) == 15
  assert exponential_series(1, 5) == 6
  assert exponential_series(0, 10) == 1
  assert exponential_series(3, 0) == 1
  assert exponential_series(5, 2) == 31
output: def exponential_series(x, n):
      result = 0
      for i in range(n + 1):
          result += x ** i
      return result