This is a java program for happy number but before that what is a happy number.

A number whose sum of the square of digits is **ultimatly **equal to 1 is a happy number. By ultimately we mean that starting with any positive number we continue the addition of square of digits till we get a single digit number (0 ~ 9). But the on whose sum is ultimately 1 is a happy number.

**Example #1:**13 ; 1

^{2}+ 3

^{2}= 1 + 9 =10 ; 1

^{2}+ 0

^{2}= 1 (Thus a happy number)

**Example #2:**32; 3 2 + 2 2 = 9 + 4 = 13; and in Example#1 13 is already a happy number;

Some of the first happy numbers are: 1, 7, 10, 13, 19, 23, 28, 31, 32, 44, 49, 68, 70, 79, 82, 86, 91, 94, 97, 100, 103, 109, 129, 130.

**Java program to check for a happy number**

**Java program to check for a happy number**

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import java.io.*; class happynumber { public static void main(String args[])throws Exception { int i,j; happyno obj=new happyno(); BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); System.out.print("enter a number : "); i=Integer.parseInt(br.readLine()); while((j=obj.happy(i))/10!=) // You have to check the sum of all digits until a single digit is achieved i.e. sum=1,2,3,..9 { i=j; // If sum of digits= 19 it then again goes to 1+9 =10 and again 1+0= '1' a single digit to check if 1 or not } if ( j==1) System.out.println("It is a happy number "); else System.out.println("Not a happy number"); } int happy(int n) { if(n/10==) return n*n; else return (int)Math.pow(n%10,2)+ happy(n/10); } } |

**OUTPUT:**

*Incoming terms:* Java program to check a happy number, program to check for a happy number.