When counting, count to dozens, and you want to know what the next integer is.
When counting, the numbers 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, … are called natural numbers. Natural numbers have two meanings: quantity and order, which are divided into cardinal number and ordinal number. The basic unit is 1, and the counting units are 10, 100, 1000, 1000, 10000.
classify
According to "divisible by 2", it can be divided into odd and even numbers. According to the number of factors, it can be divided into prime numbers and composite numbers.
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 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, namely ordinal number theory and cardinal number theory, which made the concept, operation and related properties of natural numbers strictly discussed.