In this tutorial, we will write a java program to check whether a given number is **Neon number** or not. We will also write a program to find all the **Neon numbers in a given range**.

## What is a Neon Number?

A number is called Neon number if sum of digits of its square is equal to the number itself. For example 9 is a neon number because:

Original Number = 9 Square of 9 = 9 X 9 = 81 Sum of digits of its square = 8+1 = 9 = Original Number

Similarly 1 is also a neon number because:

Original number = 1 Square of 1 = 1 X 1 = 1 Sum of digits of its square = 1 = original number

## Java Program to check if a number is Neon Number

The steps to **check for Neon number** are:

- Read the number input by user.
- Calculate the square of the input number.
- Calculate the sum of digits of square.
- Compare the sum of digits of square and number, if both the equal then display “
**Neon Number**” else display “**Not a Neon Number**“.

import java.util.*; public class JavaExample { public static void main(String args[]) { int sumSquareDigits=0, num; Scanner scanner = new Scanner(System.in); System.out.print("Enter a number: "); //Reading user input and storing into variable num num = scanner.nextInt(); scanner.close(); int square = num * num; //Finding the sum of digits of square while(square != 0) { //getting last digit of square int lastDigit = square % 10; //adding the last digit to the sumSquareDigits sumSquareDigits = sumSquareDigits + lastDigit; //removing last digit from square to repeat the process //for second last digit and so on square = square / 10; } //comparing the number with sum of digits of square if(num == sumSquareDigits) System.out.println(num + " is a Neon Number."); else System.out.println(num + " is not a Neon Number."); } }

**Output:**

Enter a number: 9 9 is a Neon Number.

## Program to find all Neon Numbers in a Given Range

In this program, we are finding all the Neon numbers in a given range. The user enters the start and end range, we then run a loop from start range till end range and for each number between this range, we call the `checkNeon()`

method. This method checks whether the number is Neon number or not. If the number is Neon it gets displayed else it gets skipped.

import java.util.*; public class JavaExample { static boolean checkNeon(int num) { int square = num * num; int sumSquareDigits = 0; while (square != 0) { sumSquareDigits = sumSquareDigits + square % 10; square = square / 10; } return sumSquareDigits == num; } public static void main(String args[]) { int startRange, endRange; Scanner scanner = new Scanner(System.in); System.out.print("Enter the Starting Range: "); startRange = scanner.nextInt(); System.out.print("Enter the Ending Range: "); endRange = scanner.nextInt(); System.out.print("All Neon numbers between "+startRange+ " and "+endRange+" are: "); for (int i = startRange; i <= endRange; i++) if (checkNeon(i)) System.out.print(i+" "); } }

**Output:**

Enter the Starting Range: 1 Enter the Ending Range: 500 All Neon numbers between 1 and 500 are: 1 9

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