Primorial of a number

Question

Given a number n, the task is to calculate its primorial. Primorial (denoted as Pn#) is product of first n prime numbers. Primorial of a number is similar to factorial of a number. In primorial, not all the natural numbers get multiplied only prime numbers are multiplied to calculate the primorial of a number. It is denoted with P#.

Examples:

Input: n = 3
Output: 30 
Priomorial = 2 * 3 * 5 = 30

As a side note, factorial is 2 * 3 * 4 * 5

Input: n = 5
Output: 2310
Primorial = 2 * 3 * 5 * 7 * 11 

The way I think to solve this problem is:

1. Write a isPrime function to test whether the number is a prime number.
2. Write a fuction(int n) that can print n number of prime,
   e.g. n=3, then print 2,3,5 three prime numbers.
3. Multiply all the prime numbers together.

However, I am stuck into the step two. Please help me to solve this problem, or if there is any better way, please tell me.

edit: following is my code, I just go to the step two so far. But when I try to test the countPrime function, the output is 0.

public class PrimorialNum {

static boolean isPrime(int n) {
    for (int i = 2; i <= Math.sqrt(n); i++) {
        if (n % i == 0) {
            return true;
        }
    }
    return false;
}

static int countPrime(int k) {
    int count = 0;
    int x=0;
    while (x >= 2) {
        if (isPrime(x)) {
            count++;
        }
        x++; 
        System.out.println(x);
    }
    return count;
}

public static void main(String[] args) {
    System.out.println(countPrime(2));

}

}

Answer 1

I think this might work for you, did not have the possibility to try it myself right now. If k > 0.

1. isPrime()

   static boolean isPrime(int n) {
    for (int i = 2; i < n; i++) {
           if (n % i == 0 && i != n) return false;
       }
   return true;
   }
   

2.Just print

static void countPrime(int k) {
 int x = 2;
 int primesFound = 0;
 while (primesFound != k) {
  if (isPrime(x)) {
   System.out.print(x);
   primesFound++;
  }
  x++;
 }
}

3.Multiply

static int countPrime(int k) {
 int count = 2;
 int x = 3;
 int primesFound = 1;
 while (primesFound != k) {
  if (isPrime(x)) {
   count = count * x;
   primesFound++;
  }
  x++;
 }
return count;
}