I have taught myself number theory since junior high school, relying on competition books. In high school, there are textbooks besides competition books. Universities and libraries have a lot of materials, and they are still looking for materials to study online. ○: First of all, we should understand the meaning of number theory. There is no doubt that number theory is the mother, source, destination and crown of mathematics. If people want to become gods and buddhas alive, they must strengthen the study of number theory when learning mathematics. Have absolute confidence in yourself; Familiar with and flexible use of basic concepts, but have the idea of promotion and extension; To cultivate inspiration or so-called understanding, try to solve multiple problems (extension); To a certain extent, we should cultivate our own style and demeanor, aspire to become a master, and sort out or unify some messy contents within a certain range. 1. There are some knowledge of number theory in the math contest book, such as divisible prime numbers (prime numbers, composite numbers), divisor multiples, greatest common factor (gcd), least common factor (lcm), division by turns (Euclid algorithm), Fermat theorem, Euler function theorem, Wilson theorem, China remainder theorem (Sun Tzu theorem, China's birth theorem, I have some improved schemes). Like a drowning bear