Perfect Number Program in Java Using While Loop

The number which is equal to the sum of its divisors is called a perfect number. Read the entered long number, assigned to the long variable n. While loop iterates until the condition (i<=n/2) is false. If the remainder of n/i=0 then add i value to the sum and increase the i value. After all the iterations compare the number with the sum, if both are equal then prints the number as a perfect number.

Example:

n = 6, i = 1 condition at while is 1 <= 3 is true, here 6%i = 0 is true so sum = 1,

i = 2, 2 < 3 is true, 6%2 = 0 is true so sum = 1+2=3,

i=3, 3<=3 is true, 6%3=0 is true so sum=3+3=6, for i=4 the while loop terminates and compares the sum value with n, both are equal, so it prints 6 is a perfect number.

Implementation

Java

import java.util.Scanner;

class Perfect
{
    public static void main(String arg[])
    {
        long n,sum=0;
                     Scanner sc=new Scanner(System.in);
        System.out.println("Enter a number");
                   n=sc.nextLong();
        int i=1;
        while(i<=n/2)
        {
           if(n%i==0)
           {
        sum+=i;
           }
          i++;
        }
    if(sum==n)
    {
    System.out.println(n+" is a perfect number");
               }
    else
    System.out.println(n+" is not a  perfect number");
    }
}

Output:

The time complexity is O(n), where n is the input number.

The auxiliary space is O(1)

Example :

Java

import java.io.*;
public class PerfectNumber {
    public static void main(String[] args) {
        int number = 1;

        while (number <= 10000) {
            int sum = 0;

            // Find all the factors of the current number and add them up
            for (int i = 1; i < number; i++) {
                if (number % i == 0) {
                    sum += i;
                }
            }

            // If the sum of the factors equals the number, it's a perfect number
            if (sum == number) {
                System.out.println(number + " is a perfect number");
            }

            number++;
        }
    }
}

output :

6 is a perfect number
28 is a perfect number
496 is a perfect number
8128 is a perfect number