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?

找规律。

右上角(2n+1)^2

左上角(2n+1)^2-(2n+1)+1

左下角(2n+1)^2-4*n

右下角(2n+1)^2-6*n

2n+1<=1001    n<=500

#include <iostream>

#include <string>

using namespace std;

int main()

{

	int n = 500;

	long long res = 1;

	for (int i = 1; i <= 500; i++)

	{

		int tmp = (2 * i + 1)*(2 * i + 1);

		res += tmp*4 - (2 * i + 1) + 1 - 4 * i - 6 * i;

	}

	cout << res << endl;

	system("pause");

	return 0;

}