Java: Find and print the first 10 happy numbers

Last update on March 11 2025 11:10:11 (UTC/GMT +8 hours)

First 10 Happy Numbers

Write a Java program to find and print the first 10 happy numbers.

Happy number: Starting with any positive integer, replace the number by the sum of the squares of its digits, and repeat the process until the number equals 1, or it loops endlessly in a cycle which does not include 1.

Example: 19 is a happy number
1² + 9²=82
8² + 2²=68
6² + 8²=100
1² + 0² + 0²=1

Pictorial Presentation:

Sample Solution:

Java Code:

import java.util.HashSet;
public class Example9 {
public static void main(String[] args){
	System.out.println("First 10 Happy numbers:");
       for(long num = 1,count = 0;count<8;num++){
           if(happy_num(num)){
               System.out.println(num);
               count++;
           }
       }
}
   public static boolean happy_num(long num){
       long m = 0;
       int digit = 0;
       HashSet<Long> cycle = new HashSet<Long>();
	   while(num != 1 && cycle.add(num)){
           m = 0;
           while(num > 0){
               digit = (int)(num % 10);
               m += digit*digit;
               num /= 10;
           }
           num = m;
       }
       return num == 1;
   }   
 }

Sample Output:

First 10 Happy numbers:                                                                                       
1                                                                                                  
7                                                                                                  
10                                                                                                  
13                                                                                                  
19                                                                                                  
23                                                                                                  
28                                                                                                  
31

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Java program to generate happy numbers using iterative reverse-and-square-sum with cycle detection.
• Write a Java program to display the transformation sequence for a given happy number candidate.
• Write a Java program to count happy numbers within a user-specified range using functional programming techniques.
• Write a Java program to optimize happy number detection by caching previously computed intermediate sums.

Java Code Editor:

Contribute your code and comments through Disqus.

Previous: Write a Java program to print out the first 10 Catalan numbers by extracting them from Pascal's triangle.
Next: Write a Java program to check whether a given number is a happy number or unhappy number.