Java: Program to start with an integer n, divide n by 2 if n is even or multiply by 3 and add 1 if n is odd, repeat the process until n = 1

Last update on May 12 2025 13:11:33 (UTC/GMT +8 hours)

Collatz Conjecture Simulation

Write a Java program starting with an integer n, divide it by 2 if it is even, or multiply it by 3 and add 1 if it is odd. Repeat the process until n = 1.

Sample Solution:

Java Code:

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        // Prompt the user to input the value of n
        System.out.println("Input the value of n: ");
        
        // Create a Scanner object to read user input
        Scanner in = new Scanner(System.in);
        
        // Read an integer from the user
        int n = in.nextInt();
        
        // Continue looping until n becomes 1
        while (n != 1) {
            // Check if n is even
            if (n % 2 == 0) {
                n = n / 2; // If even, divide n by 2
            } else {
                n = (3 * n + 1) / 2; // If odd, perform a calculation
            }
        }
        
        // Print the final value of n
        System.out.println("\nValue of n = " + n);
        
        // Close the Scanner
        in.close();
    }
}

If input 5

Sample Output:

Input the value of n: 
 9

Value of n = 1

Flowchart:

For more Practice: Solve these Related Problems:

• Modify the program to count the number of steps to reach 1.
• Write a program to print the entire sequence instead of just the result.
• Modify the program to find the longest Collatz sequence under 1000.
• Write a program to visualize the Collatz sequence as a graph.

Go to:

• Java Basic Programming Exercises Home ↩
• Java Exercises Home ↩

PREV : String Starts with Word.
NEXT : Digit Sum in Words.

Java Code Editor: