Factor: Integer A can be divisible by Integer B, A is called multiple of B, and B is called factor or prime number of A,

Example: 6 ÷ 2 = 3 1, 2,3,6 is a factor of 6.

The factors of 6 are: 1, 2, 3, 6.

Plural number: plural number refers to

① The greatest common divisor between two numbers is only the product of those two numbers of 1;

② The common divisor between two numbers is not only 1. Multiplying one of the divisors by the smallest number can be divisible, and the multiplied number is the composite number.

A composite number, also called a composite number, is a positive integer that satisfies one of the following (equivalent) conditions:

1. is the product of two integers greater than 1;

2. There is a factor)； greater than 1 and less than itself;

3. There are at least three factors (factors);

4. It is neither 1 nor a prime number (prime number);

5. Non-prime numbers with at least one prime factor.

6. The product of two or more prime numbers can form a composite number, and only a composite number can be formed. On the contrary, a composite number can be divided into a product of a group of prime numbers, and only into a product of a group of prime numbers. That is to say: the composite number formed by the product of more than three prime numbers cannot be regarded as the product of two prime numbers! (It can also be said that there are other factors besides 1 and itself.)