1, factor and multiple: If the integer A is divisible by B, then A is a multiple of B, and B is a factor of A. ..

2. How to find the factors of a number: the number of factors of a number is limited, the smallest is 1, and the largest is itself. The method is to look for it in sequence.

3. How to find the multiple of a number: the number of multiples of a number is infinite, the smallest is itself, and there is no maximum. When using the method, multiply the natural number in turn.

Features of multiples of 4, 2, 5 and 3: Numbers with 0, 2, 4, 6 and 8 in the unit are multiples of 2. Numbers with 0 or 5 in units are multiples of 5. The sum of the numbers on each digit of a number is a multiple of 3, and this number is a multiple of 3.

5. Prime number and composite number: a number. If there are only two factors of 1 and itself, it is called a prime number, and the smallest prime number is 2. A number, if there are other factors besides 1 and itself, is called a composite number, and the smallest composite number is 4.