input: Write a function to calculate an exponential series for a given number x and a specified number of terms n. The function should return the sum of the series up to the nth term.
  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(0, 10) == 1
  assert exponential_series(3, 0) == 1
  assert exponential_series(5, 1) == 6
output: def exponential_series(x, n):
      sum = 0
      for i in range(n+1):
          sum += x ** i
      return sum