input: Write a function to calculate an exponential series. The function should take two parameters: x (the base) and n (the number of terms). It should return the sum of the series up to the nth term.
  assert exponential_series(2, 3) == 15
  assert exponential_series(3, 2) == 13
  assert exponential_series(4, 0) == 1
  assert exponential_series(1, 5) == 6
output: def exponential_series(x, n):
      result = 0
      for i in range(n + 1):
          result += x ** i
      return result