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