1, odd× odd = odd, even× even = even, odd× even = even.

2. Odd number ÷ odd number = odd number or fraction, even number ÷ even number = even number or fraction (dividend is not zero), odd number ÷ even number = fraction (dividend is not zero).

3. Even number ÷ odd number = fraction.

Regarding even and odd numbers, there are the following properties:

(1) Two consecutive integers must be odd and even.

(2) The sum or difference between odd numbers is even; The sum or difference between even and odd numbers is odd; The sum of any number of even numbers is even; The sum of odd numbers is odd; The sum of even and odd numbers is even.

(3) The sum or difference of two odd (even) numbers is even; The sum or difference between even and odd numbers must be odd numbers.

(4) All positive even numbers except 2 are composite numbers.