cube.java

import java.util.*;

class Test{

	public static void main(String[] args){
		int n,c;
		Scanner sc = new Scanner(System.in);
		System.out.print("Enter a negative integer: ");
		n = sc.nextInt();
		if(n>0){
			System.out.println("Enter a -ve integer.");
			return;
		}
		c= cube(n);
		System.out.println("Cube(n)= "+c);
	}

	private static int cube(int n){
		if(n==0)
			return 0;
		return cube(n+1) + -3*n*n - 3*n -1;
	}

}