BigInteger

BigInteger bi=Bigger.Parse("999999999999999999999999999999999999999999999999999999999999999999999999999999");

Console.WriteLine(bi);

Console.WriteLine(bi.IsEven);

Console.WriteLine(bi.IsOne);

BigInteger big=BigInteger.Multiply(bi,BigInteger.Parse("999999999999999999999999999999999999999999999999999999"));

Console.WriteLine(big);