Java Program to Check Goldbach Number

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In the previous article, we have discussed Java Program to Check Triangular Number

In this article we are going to understand what Triangular number is and how we can check whether a number is Triangular or not in Java with examples.

Program to Check Goldbach Number

Goldbach numbers are even integer numbers that can be divided into two odd primes. (All integers above 4 are GoldBach Number.)

Example :

6    =  3+3
16  =  13 + 3

In the above examples the numbers are Goldbach numbers as they are sum of two odd primes.

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Approach :

  1. Enter/declare a number and store it .
  2. We check whether the number is greater than 4 or not, if not it is not a Goldbach number.
  3. Then we start subtracting the prime numbers from this, until we find another prime.
  4. If two primes are found then that number is said to be a Goldbach Number.

Program:

import java.util.Scanner;
public class GoldbachNumber{
    public static void main(String args[])
    {
        //Taking the number as input from the user using scanner class
        Scanner scan = new Scanner(System.in);
        System.out.print("Enter a number : ");
        int num = scan.nextInt();

        int temp;
        boolean flag = false;
        // Checks if the number is above 4 then goes into the loop
        if(num>4)
        {
            // Runs a loop from 3 to the num until the break condition is met
            for(int i = 3; i<num; i+=2)
            {
                // Checks whether the current number is prime else goes out
                if(isPrime(i))
                {  
                    // Finds the other number and checks if it is prime number
                    temp = num - i;
                    if(isPrime(temp))
                    {
                        flag = true;
                        break;
                    }
                }
            }
        }
        if(flag)
        {
            System.out.println(num+" is a Goldbach number");
        }
        else
        {
            System.out.println(num+" is Not a Goldbach number");
        }

    }

    // Function to check for prime
    static boolean isPrime(int num)
    {
        int iter = 2;
        boolean flag = true;
        while (num > iter)
        {
            if (num % iter == 0)
            {
                flag = false;
                break;
            }
            iter++;
        }
        return flag;
    }
}

Output:

Enter a number : 16
16 is a Goldbach number

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