multiThreading notify and Wait() concept?

Question

Here is the code for fecthing the primenumbers till 100 and storing them in an array. But the problem is the code is not working properly because the second for loop is not waiting till the i is changed. Can anybody help me to figure out what the problem is?

       synchronized (this) {
        boolean stop = false;
        boolean change = false;
        int primenumber[]= new int[20];
        System.out.println("The prime numbers are : ");
        for (int i = 1; i <= 100; i++) {
            int count = 0;
            change = true;
            notify();
            for (int num = i; num >= 1; num--) {
                if (i % num == 0) {
                    count = count + 1;
                }
            }
            if (count == 2) {
                if (!stop) {
                    for (int ab = 0; ab <= 20; ab++) {
                        primenumber[ab] = i;
                        while (!change) {
                            try {
                                wait();
                            } catch (InterruptedException e) {
                            }
                        }
                    }
                }
            }
        }
    }

Answer 1

int num = 0;
    System.out.println("Please Enter n.");
    Scanner scanner = new Scanner(System.in);
    int n = scanner.nextInt();
    scanner.close();

    System.out.println("\nPrime Numbers up to " + n + ".");

    for (int i = 1; i <= n; i++) {
        int counter = 0;
        for (num = i; num >= 1; num--) {
            if (i % num == 0) {
                counter++;
            }
        }

        // Counter = 2 means number is only divisible by 1 and the number itself. So it's a prime number.
        if (counter == 2) 
        {
            System.out.print(i + " ");
        }
    }