If a number is a multiple of 2, it is even and can be expressed as 2n; Otherwise, it is an odd number, which can be expressed as 2n+ 1(n is an integer), that is, the remainder of odd number divided by two is 1.
0 is a special even number, which is not only the dividing line between positive even number and negative even number, but also the watershed between positive odd number and negative odd number.
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.
(5) The greatest common divisor of adjacent even numbers is 2, and the least common multiple is half of their product.