Number theory in Zhu Chunli's junior high school mathematics competition
These two books are ok, but they are all systematic explanations of number theory, which are suitable for you who are interested in learning slowly in the future.
The competition is very utilitarian, and there are many investigations on the application of knowledge, so the foundation is not too high, which is a bit like pulling out the seedlings.
Don't take part in any Olympic math competition without special needs, which is purely encouraged by some teachers, in order to earn some extra money for training. Cramming teaching disrupts students' normal learning rhythm. Before the whole knowledge system has undergone a qualitative change, blindly attacking a certain subject or field will lead to the slightest and best result. In most cases, it will dampen students' enthusiasm and annihilate their interest in future study, which can be described as harmful and slightly beneficial. China's education is in the wrong direction. Are you still alive when you walk into a dead end?