new_contents: #!/usr/bin/env python
  #-*-coding:utf-8-*-
  
  '''
  Starting with the number 1 and moving to the right
  in a clockwise direction a 5 by 5 spiral is formed as follows:
  
  21 22 23 24 25
  20  7  8  9 10
  19  6  1  2 11
  18  5  4  3 12
  17 16 15 14 13
  
  It can be verified that the sum of the numbers on the diagonals is 101.
  What is the sum of the numbers on the diagonals
  in a 1001 by 1001 spiral formed in the same way?
  '''
  
  import timeit
  
  
  def loop(limit):
      total = 1 + 24
      prev = 24
      for i in range(3, (limit+3)/2):
          delta = 20 + 32 * (i - 2)
          current = delta + prev
          total += current
          prev = current
      return total
  
  
  if __name__ == '__main__':
      print loop(1001)
      print timeit.Timer('problem_028.loop(1000)', 'import problem_028').timeit(10)
  
subject: add problem 28