bool IsPrime(BigInteger Num)
        {
            if (Num < 2) return false;
            else if (Num < 4) return true;
            else if (Num % 2 == 0) return false;
            else for (BigInteger u = 3; u * u <= Num; u += 2)
                    if (Num % u == 0) return false;
            return true;
        }

bool IsPrimeBetter(BigInteger Num)
        {
            ulong arrayLe = (ulong)Isqrt((long)Num);
            if (Num < 2) return false;
            else if (Num < 4) return true;
            else foreach (var prime in new Atkin(arrayLe))
                    if (Num % prime == 0) return false;
            return true;
        }