input: def sierpinski_triangle(n):
      """
      Generate the first n elements of the Sierpinski triangle.
      
      >>> sierpinski_triangle(6)
           1 
          1 0 
         1 1 1 
        1 0 0 0 
       1 1 1 1 1 
      1 0 0 0 0 0 
      """
output:     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)
      
      max_width = len(' '.join(map(str, triangle[-1])))
      
      for row in triangle:
          row_str = ' '.join(map(str, row))
          print(row_str.center(max_width))