Question

JustPerfects.java (for Loop).

In this program, you will use loops to identify perfect numbers (a number equal to the sum of its divisors - 6 and 28 are the first two! 6 is 2 +3 + 1 and 28 is 14+7+4+2+1). Being the perfect number is quite unique. Only 4 perfect numbers exist between 1 and 10,000 and you’ve already found two! Please write a program to find the additional pair.

Bonus: How many perfect numbers exist between 10,000 and 35,000? (+2)

Answer 1

public class JustPerfects {

    public static void main(String[] args) {
        for (int i = 1; i <= 10000; i++) {
            int sum = 0;
            for (int j = 1; j < i; j++) {
                if (i % j == 0)
                    sum += j;
            }
            if (sum == i) {
                System.out.println(i);
            }
        }
        int count = 0;
        for (int i = 10000; i <= 35000; i++) {
            int sum = 0;
            for (int j = 1; j < i; j++) {
                if (i % j == 0)
                    sum += j;
            }
            if (sum == i) {
                ++count;
            }
        }
        System.out.println("Number of perfect numbers between 10,000 and 35,000 is " + count);
    }
}