（Problem 28）Number spiral diagonals

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?

#include<stdio.h>#include<string.h>#include<math.h>#include<ctype.h>#include<stdlib.h>#include<stdbool.h>void countSum(){int i=3;int sum=1;int n=(1001+1)/2-1;while(n--){int t=i*i;sum+=(4*t-(i-1)*6);i=i+2;}printf("%d\n",sum);}int main(){countSum();return 0;}

Answer:

669171001