Java Program to Check Peterson Number

Last Updated: 16 April, 2023

On this tutorial page, we are going to learn how to write a Java program to check whether a number is peterson or not.

A Peterson number is a number that can be expressed as the sum of the factorials of its digits in a given base. In other words, if a number "n" in base "b" is equal to the sum of the factorials of its digits "d1, d2, ... dk", then it is called a Peterson number.

For example, 145 is a Peterson number in base 10, since 1! + 4! + 5! = 1 + 24 + 120 = 145.

Here's a Java program to check if a given number is a Peterson number:

Example: Check the given number is Peterson or not in Java

  
  import java.util.Scanner;
  public class PetersonNumber {
    // a predefined array for the quickly find the factorial
    static int[] factorial = new int[] { 1, 1, 2, 6, 24, 120, 720, 5040, 
                                         40320, 362880, 3628800, 39916800, 479001600 };
    
    public static void main(String args[]) {
      Scanner scanner = new Scanner(System.in);
      System.out.print("Enter the number: ");
      int number = scanner.nextInt();
      scanner.close();
      
      if (isPeterson(number))
        System.out.println(number + " is a Peterson number.");
      else
        System.out.println(number + " is not a Peterson number.");
    }
    
    // function to check the given number is Peterson or not
    static boolean isPeterson(int number) {
      int num = number;
      int sum = 0;
      
      while (num > 0) {
        // getting the last digit of the number
        int lastDigit = num % 10;
        // determines the factorial of the digit and add it to the variable sum
        sum += factorial[lastDigit];
        // removing the last digit of the given number
        num = num / 10;
      }
      
      // returning boolean (true or false) as an output.
      // returns true if sum (sum of factorial of all digits) and number both are equal
      // else false
      return (sum == number);
    }
  }

In the above program, taking user input using the java.util.Scanner class and passing the number as input in the isPeterson() method and checking whether the number is Peterson or not.

In the first execution, passing 145 as an input, which is a Peterson number,

In the second execution, 234 is passed as an input, which is not a Peterson number. Both the outputs are given below.

Output 1

Enter the number: 145
145 is a Peterson number.

Output 2

Enter the number: 234
234 is not a Peterson number.