dsa

        public static bool IsPrimeMoreEfficient(BigInteger num)
        {
            if (num < 2) return false;
            if (num < 4) return true;
            if (num % 2 == 0) return false;

            for (BigInteger u = 3; u*u <= num; u += 2)
                if (num % u == 0) return false;

            return true;
        }