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 13It 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?

My solution in Ruby:

```
corners = [1]
num = 1
add = 2
500.times do
4.times do
num += add
corners << num
end
add += 2
end
sum = 0
corners.each { |c| sum += c }
puts sum
```