input: def sierpinski_triangle(n):
      """Generate the first n elements of the Sierpinski triangle.
      >>> sierpinski_triangle(6)
      Output as described in the instruction.
      """
output:     if n <= 0:
          return []
      
      triangle = [[1]]
      
      for i in range(1, n):
          row = [1]
          for j in range(1, i):
              row.append(triangle[i-1][j-1] + triangle[i-1][j])
          row.append(1)
          triangle.append(row)
      
      return triangle