Project Euler - 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 07 08 09 10
19 06 01 02 11
18 05 04 03 12
17 16 15 14 13

It can be verified that the sum of the numbers on the diagonals (CM: in bold) is 101.

What is the sum of the numbers on the diagonals in a 1001 by 1001 spiral formed in the same way?