In this tutorial, we will learn about the Peterson number and check if the number is Peterson or not in java.

## What is Peterson Number?

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

**Example**:

`Number = 145`

145 = !1 + !4 + !5

= 1 + 4*3*2*1 + 5*4*3*2*1

= 1+24+120

= **145 =145**

Therefore, we can see that after the sum of the factorial of 145 is equal to the number 145 itself. Hence the Peterson Number.

**Java Program to check whether the number is Peterson Number or not**

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 | import java.io.*; import java.util.*; public class GFG { // find factorial of digits static int[] fact = new int[] { 1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880 }; //function static boolean peterson(int num) { int n = num; int sum = 0; while (num > 0) { int digit = num % 10; sum += fact[digit]; num = num / 10; } return (sum == n); } // main Program static public void main(String[] args) { int num; Scanner sc = new Scanner(System.in); System.out.print("Enter a number: "); num = sc.nextInt(); if (peterson(num)) System.out.println(num + " is a Peterson number"); else System.out.println(num + " is not a Peterson number"); } } |

**Output 1:**

`Enter a number: 145 `

145 is a Peterson number

**Output 2:**

`Enter a number: 55 `

55 is not a Peterson number