FriendsNumbers.java

import java.util.Scanner; // to read data

public class FriendsNumbers {

    /**
    *   Program:    FriendsNumbers.java
    *   Purpose:    Solve maths problem for Yahoo! Answers
    *   Creator:    Chris Clarke
    *   Created:    04.10.2013
    */

/*
 The sum of all natural ( positive integer ) number of dividers 220 , except
himself , is equal to
1 2 4 5 10 11 20 22 44 55 110 = 284
and the sum of all natural number of dividers 284 , except himself
shall be equal to
1 2 4 71 142 = 220 .
Find even such a pair of numbers . "
The numbers 220 and 284 numbers called friends . Generally , we
To say that two positive integers are friends if each of them equal
with the sum of all of the other physical dividers , including 1.
Write the program in Java that solves the problem of finding all pairs
Friends of numbers from 2 to N. The program accepts as input the number N and
to calculate and print all your friends numbers from 2 to N.
*/

    public static void main (String[] args) {

        Scanner scan = new Scanner (System.in);

        int n, sum1=0, sum2=0;
        System.out.print("Enter number N: ");
        n = Integer.parseInt(scan.nextLine());
        System.out.println();
        for (int i=2; i<=n; i++) {
            sum1=0;
            sum2=0;
            for (int j=1; j<i; j++) {
                if (i%j==0) {
                    sum1+=j;
                }
            }

            for (int j=1; j<sum1; j++) {
                if (sum1%j==0) {
                    sum2+=j;
                }
            }

            if (sum2 == i && sum1 < sum2) {
                System.out.println(sum1+" and "+sum2+" are friends numbers");
            }
        }
    } // end main

} // end class