1, factor: the number of factors of a number is limited, the smallest factor is 1, and the largest factor is itself.

How to find the factor of a number: find it in order in pairs or by division.

2. Multiplication: The number of multiples of a number is infinite, and the smallest multiple is itself.

Solution of multiple of a number: multiply natural numbers in turn.

3. Natural numbers can be divided into odd numbers and even numbers according to whether they are divisible by 2.

Odd number: Numbers that are not multiples of 2 are called odd numbers.

Even number: A number that is a multiple of 2 is called even number.

The smallest odd number is 1 and the smallest even number is 0.

4. Composite number: a number. If there are other factors besides 1 and itself, such a number is called a composite number. For example, 4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 22 are all complex numbers.

5, common factor, the greatest common factor.

The common factor of several numbers is called the common factor of these numbers. The biggest factor is called their greatest common factor. Decomposition of prime factors by short division (a composite number is written in the form of multiplication of several prime numbers) Example: 12=2×2×3.