// Fills the array with the first array.length prime numbers;
    // assumes that each array entry at an index below n is already correctly set.
    private static void primes(int[] array, int n) {
        if (n < array.length) {
            if (n == 0) {
                array[0] = 2;
                primes((array), (n+1));
            } else {
                int check = array[n - 1];
                boolean isPrime;
                do {
                    check++;
                    isPrime = true;
                    for (int i = 0; i < n; i++) {
                        isPrime = isPrime && (check % array[i] != 0);
                    }
                } while (! isPrime);
                array[n] = check;
                primes((array), (n+1));
            }
        }
    }