private static boolean[] getArePrimesArray(int to) {
        boolean[] primes = new boolean[to + 1];

        for (int i = 0; i < primes.length; i++) {
            primes[i] = true;
        }

        int toSqrt = (int) Math.floor(Math.sqrt(to));

        for (int index = 2; index <= toSqrt; index++) {
            if (primes[index] == true) {
                for (int j = index * index; j <= to; j += index) {
                    primes[j] = false;
                }
            }
        }

        return primes;
    }