ProjectEuler/P028.py at master · mcleu/ProjectEuler · GitHub

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# -*- 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?
#==============================================================================


n = 1
delta = 2
dsum = 1

nmax = 1001**2

while (n < nmax):
    for ii in range(4):
        n += delta
        dsum += n
    delta += 2

print dsum
# 669171001