Perfect number

A number is called perfect if the number is equal to the sum of its divisors (the number itself is not considered a divisor in this case).

Check Perfect Number

The above code checks if a given number is a perfect number or not. A perfect number is a positive integer that is equal to the sum of its proper positive divisors, excluding the number itself.

It first takes the number as input using the Scanner class. It then initializes the sum variable with 0.

It then uses a for loop to find the sum of all positive divisors of the given number. The loop starts from 1 and continues till the number, and for each iteration, it checks if the number is divisible by i (the current iteration value). If the number is divisible, then the value of i is added to the sum.

After the loop ends, the code checks if the sum is equal to the given number. If yes, then the number is considered as a perfect number, and a message is displayed saying so. If the sum is not equal to the number, then the number is not a perfect number, and a message is displayed accordingly.

import java.util.Scanner;

public class PerfectNumber {
	public static void main(String[] args) {
		Scanner reader = new Scanner(System.in);
		int number, sum = 0;

		System.out.println("Enter a number to check for perfect: ");
		number = reader.nextInt();
		reader.close();

		for (int i = 1; i < number; i++) {
			if (number % i == 0) {
				sum = sum + i;
			}
		}

		if (sum == number) {
			System.out.print(number + " is a perfect number");
		} else {
			System.out.print(number + " is not a perfect number");
		}
	}
}

Output

Enter a number to check for perfect: 28
28 is a perfect number

Perfect Number List (1-n)

This Java program calculates and displays the perfect numbers within a given range (up to an upper bound max). The program defines a function checkPerfect which takes the maximum limit as input and calculates the perfect numbers within the given range. The program first defines an integer variable number and sets it equal to the minimum value min (which is set to 1). Then, using a for loop, the program iterates number from min to max. For each iteration, the program initializes sum to 0 and i to 1. Then, using a nested for loop, the program iterates i from 1 to number-1, and adds i to sum if number is divisible by i. Finally, if sum equals number, the program prints number and the message “is a perfect number”.

The main function reads the upper bound value from the user, calls the checkPerfect function with the upper bound as an argument, and then closes the Scanner object.

import java.util.Scanner;

public class PerfectNumberSeries {
	private static void checkPerfect(int max) {
		int number, min = 1, i, sum = 0;

		for (number = min; number <= max; number++) {
			sum = 0;
			for (i = 1; i < number; i++) {
				if (number % i == 0) {
					sum = sum + i;
				}
			}
			if (sum == number) {
				System.out.println(number + " is a perfect number");
			}
		}
	}

	public static void main(String[] args) {
		Scanner reader = new Scanner(System.in);
		int max;

		System.out.print("Enter the upper bound to find perfect numbers: ");
		max = reader.nextInt();
		reader.close();

		checkPerfect(max);
		
	}
}

Output

Enter the upper bound to find perfect numbers: 10000
6 is a perfect number
28 is a perfect number
496 is a perfect number
8128 is a perfect number