28 Number spiral diagonals - Project Euler +

package xxx.xxx.xxx;
/*
 * 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?
 */
public class NumberSpiralDiagonals {

private void compute(int length){
int middlepoint = length/2+1-1;
int i = 1;
int sum = 1;
System.out.println("("+middlepoint+","+middlepoint+")");
while(i<=length/2){
// sum = sum +((2*i+1)*(2*i+1)-6*i)+((2*i+1)*(2*i+1)-4*i)+((2*i+1)*(2*i+1)-2*i) +(2*i+1)*(2*i+1);
sum = sum +(2*i+1)*(2*i+1)*4-12*i;
i++;
}
System.out.println(sum);
}



/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
long startTime = System.currentTimeMillis();
NumberSpiralDiagonals n = new NumberSpiralDiagonals();
n.compute(1001);
long endTime = System.currentTimeMillis();
System.out.println("execution time " + (endTime - startTime + "ms"));
}


}