input: Write a function to generate the first n elements of the Sierpinski triangle. If the input n is negative, return an empty list.
  def sierpinski_triangle(n):
      if n < 0:
          return []
      output = []
      for i in range(n):
          output.append('1' * (2**i))
      return output
  
  assert sierpinski_triangle(6) == ['1', '11', '1111', '11111111', '1111111111111111', '11111111111111111111111111111111']
  assert sierpinski_triangle(-1) == []
  assert sierpinski_triangle(0) == []
  assert sierpinski_triangle(3) == ['1', '11', '1111']
output: def sierpinski_triangle(n):
      if n < 0:
          return []
      output = []
      for i in range(n):
          output.append('1' * (2**i))
      return output