input: Write a function to calculate an exponential series. Given a value for 'x' and the number of terms 'n', the function should return the sum of the series where each term is 'x' raised to the power of its index.
  
  def exponential_series(x, n):
      sum = 0
      for i in range(n + 1):
          sum += x ** i
      return sum
  
  assert exponential_series(2, 3) == 15
  assert exponential_series(3, 2) == 13
  assert exponential_series(4, 1) == 5
  assert exponential_series(5, 0) == 1
output: def exponential_series(x, n):
      sum = 0
      for i in range(n + 1):
          sum += x ** i
      return sum