A number used to measure the number of things or to indicate the order of things. That is, the numbers represented by the numbers 0, 1, 2, 3, 4, and ... the numbers representing the number of objects are called natural numbers, and they form an infinite group one by one from 0 (inclusive).

classify

(1) according to whether it can be divisible by 2 points.

It can be divided into odd and even numbers.

1, odd number: Numbers that are not divisible by 2 are called odd numbers.

2. Even number: The number divisible by 2 is called even number.

3. Special note: 0 is an even number. (In 2002, the International Mathematical Association stipulated that zero was even, and in 2004, China also stipulated that zero was even. Even numbers can be divisible by 2, so can 0, but the number is still 0, but it cannot be said that it has not shrunk.

(2) according to the number of factors.

It can be divided into prime numbers, composite numbers and 1.

1, prime number: only 1 and its own natural number are called prime numbers. Prime numbers are also called prime numbers.

2. Composite number: a natural number with other factors besides 1, which is itself called a composite number.

3. 1: There are only 1 factors. It is neither a prime number nor a composite number. Of course, 0 cannot calculate the factor, and it is also a non-prime number and a non-composite number.

General characteristics

A number used to measure the number of things or to indicate the order of things. That is, the numbers represented by the numbers 0, 1, 2, 3, 4, ... natural numbers start from 0, one by one, forming an infinite set.

There are addition and multiplication operations in the set of natural numbers. The result of addition or multiplication of two natural numbers is still a natural number, and subtraction or division can also be done, but the result of subtraction and division is not necessarily a natural number, so subtraction and division operations are not always effective in the set of natural numbers. Natural numbers are the most basic of all the numbers that people know.

In order to make the number system have a strict logical basis, mathematicians in the19th century established two equivalent theories of natural numbers-ordinal number theory and cardinal number theory, which made the concept, operation and related properties of natural numbers strictly discussed.