Java: Compute the sum of first n given prime numbers

Java Basic: Exercise-232 with Solution

Sum of First n Prime Numbers

Write a Java program to compute the sum of the first n prime numbers.

Input:

n ( n ≤ 10000). Input 0 to exit the program.

Visual Presentation:

Sample Solution:

Java Code:

// Importing necessary classes for input/output operations and mathematical functions
import java.util.*;

// Main class named "Main"
public class Main {
    
    // Main method to execute the program, throws IOException
    public static void main(String[] args) throws java.io.IOException {
        // Creating Scanner object to read input from the user
        Scanner scan = new Scanner(System.in);

        // Initializing variables to count prime numbers and calculate their sum
        int count = 0;
        int sum = 0;

        // Prompting the user to input a number (n<=10000) to compute the sum
        System.out.println("Input a number (n<=10000) to compute the sum:");

        // Reading the input number
        int n = scan.nextInt();

        // Looping through numbers to find prime numbers and calculate their sum
        for (int i = 2;; i++) {
            if (prime(i)) {
                count++;
                sum += i;
                // Breaking the loop when the required number of prime numbers is reached
                if (count == n) break;
            }
        }

        // Outputting the sum of the first n prime numbers
        System.out.println("Sum of first " + n + " prime numbers:");
        System.out.println(sum);
    }

    // Method to check if a number is prime
    public static boolean prime(int n) {
        // If n is 1, it is not prime
        if (n == 1) return false;

        // Checking for factors up to the square root of n
        for (int i = 2; i <= Math.sqrt(n); i++)
            if (n % i == 0) return false;

        // If no factors are found, n is prime
        return true;
    }
} 

Sample Output:

Input a number (n<=10000) to compute the sum:
100
Sum of first 100 prime numbers:
24133

Flowchart:

Java Code Editor:

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Next: Write a Java program that accept a even number (n should be greater than or equal to 4 and less than or equal to 50,000, Goldbach number) from the user and create a combinations that express the given number as a sum of two prime numbers. Print the number of combinations.