1 algorithm task

public class Test {
    public static void main(String[] args) {


        ArrayList<Integer> A = new ArrayList<>(Arrays.asList(2, 3, 9, 2, 5, 1, 3, 7, 10));
        ArrayList<Integer> B = new ArrayList<>(Arrays.asList(2, 1, 3, 4, 3, 10, 6, 6, 1, 7, 10, 10, 10));
        ArrayList<Integer> C = new ArrayList<Integer>();

        int counter;
        for (Integer i : A) {
            counter = 0;
            for (Integer j : B) {
                if (i.equals(j)) {
                    counter++;
                }
            }
            if (counter == 0 || !primeNumbers(counter)) {
                C.add(i);
            }
        }
        System.out.println(C);


    }

    public static boolean primeNumbers(int n) {
        if (n <= 1) {
            return false;

        }
        if (n == 2) {
            return true;
        }
        for (int i = 2; i <= Math.sqrt(n) + 1; i++) {
            if (n % i == 0) {
                return false;
            }
        }
        System.out.println(n);
        return true;

    }
}