Peterson_Number.java

// In this section, we will learn what is Peterson number and how can we check
// whether a given number is Peterson or not through a Java program.

// Peterson Number
// A number is said to be Peterson if the sum of factorials of each digit is
// equal to the sum of the number itself.

import java.io.*;
import java.util.*;

class Peterson_Number {
    // an array is defined for the quickly find the factorial
    static int[] factorial = new int[] { 1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880, 3628800, 39916800, 479001600 };

    // driver code
    public static void main(String args[]) {
        // constructor of the Scanner class
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter a number to check: ");
        // reading a number from the user
        int n = sc.nextInt();
        // calling the user-defined function to check Peterson number
        if (isPeterson(n))
            System.out.println("The given number is a Peterson number.");
        else
            System.out.println("The given number is not a Peterson number.");
    }

    // function to check the given number is Peterson or not
    static boolean isPeterson(int n) {
        int num = n;
        int sum = 0;
        // loop executes until the condition becomes false
        while (n > 0) {
            // determines the last digit of the given number
            int digit = n % 10;
            // determines the factorial of the digit and add it to the variable sum
            sum += factorial[digit];
            // removes the last digit of the given number
            n = n / 10;
        }
        // compares sum with num if they are equal returns the number itself
        return (sum == num);
    }
}