A natural number greater than 1 cannot be divisible by other natural numbers except 1 and itself, and is called a prime number; Otherwise it is called a composite number (it is stipulated that 1 is neither a prime number nor a composite number). The number of prime numbers is infinite.
Extended data
Although the whole prime number is infinite, there are certain rules:
1, there must be at least one prime number between a number greater than 1 and its twice (that is, within the interval (a, 2a)).
2. There is a prime arithmetic progression of any length.
3. An even number can be written as the sum of two composite numbers, and each composite number has at most 9 prime factors. (Norwegian mathematician Brown, 1920)
4. Even numbers must be written as prime numbers plus composite numbers, in which the number of factors of composite numbers has an upper bound. (Renee, 1948)
5. Even numbers must be written as a prime number plus a composite number consisting of at most five factors. Later, some people called this result (1+5) (Pan Chengdong, China, 1968).
6. A sufficiently large even number must be written as a prime number plus a composite number consisting of at most two prime factors. Short for (1+2)