Project Euler > Problem 56 > Powerful digit sum (Java Solution)

Problem:

A googol (10100) is a massive number: one followed by one-hundred zeros; 100100 is almost unimaginably large: one followed by two-hundred zeros. Despite their size, the sum of the digits in each number is only 1.

Considering natural numbers of the form, ab, where a, b [<] 100, what is the maximum digital sum?

Solution:

25164150

Code:
The solution may include methods that will be found here: Library.java .

public interface EulerSolution{

public String run();

}

/* 
 * Solution to Project Euler problem 6
 * By Nayuki Minase
 * 
 * http://nayuki.eigenstate.org/page/project-euler-solutions
 * https://github.com/nayuki/Project-Euler-solutions
 */


public final class p006 implements EulerSolution {
	
	public static void main(String[] args) {
		System.out.println(new p006().run());
	}
	
	
	private static final int N = 100;
	
	
	public String run() {
		int sum = 0;
		int sum2 = 0;
		for (int i = 1; i <= N; i++) {
			sum += i;
			sum2 += i * i;
		}
		/* 
		 * For the mathematically inclined:
		 *   sum  = N(N + 1) / 2.
		 *   sum2 = N(N + 1)(2N + 1) / 6.
		 */
		return Integer.toString(sum * sum - sum2);
	}
	
}