Problem 28

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 time

begin = time.time()

n = 1001
num = n*n
resu = 0
count = n-1
while num != 1:
	resu += 4*num-6*count
	num = num - 4*count
	count -= 2
print resu+1

end = time.time()

print end-begin