There are infinite prime numbers, also called prime numbers. A natural number greater than 1 cannot be divisible by other natural numbers except 1 and itself, in other words, this number has no other factors except 1 and itself; Otherwise it is called a composite number.
Prime number has many unique properties: (1) Prime number P has only two divisors: 1 and P(2) Basic theorem of elementary mathematics: any natural number greater than 1 is either a prime number itself or can be decomposed into the product of several prime numbers, and this decomposition is unique. (3) The number of prime numbers is infinite. (4) The number formula of prime numbers is an irreducible function. (5) If n is a positive integer, then there is at least one prime number between and. (6) If n is a positive integer greater than or equal to 2, there is at least one prime number between n and. (7) If the prime number p is the largest prime number not exceeding n (), then \ frac {n} {2} ">. (8) Among all prime numbers greater than 10, the unit number is only 1, 3, 7, 9.