Mathematically define integers: Numbers like -2,-1, 0, 1, 2 are called integers. Integer is the most basic mathematical tool that human beings can master. All integers form an integer set, which is a number ring. In an integer system, natural numbers are positive integers, 0 is zero,-1, -2, -3, …, -n, … (n is an integer) are negative integers. Positive integers, zero integers and negative integers form an integer system.

The given integer n can be negative (n∈Z-), nonnegative (n∈Z*), zero (n=0) or positive (n ∈ z+). [Edit this paragraph] Positive integer of mathematical classification.

It has been a tool for human counting since ancient times. It can be said that the process of abstracting from "one cow and two cows" or "five people and six people" into positive integers is quite natural. In fact, we sometimes call positive integers natural numbers. Zero.

It not only means "no", but also means a symbol of vacancy. In ancient China, when calculating and operating numbers with a computer chip, the vacancy was not put in the computer chip. Although there is no empty bit mark, it still creates good conditions for counting bit values and four operations. The word "zero" in Indo-Arabic numerology comes from India, which also means "empty" or "blank". Negative integer.

China first introduced negative numbers. The "positive numbers and negative numbers" discussed in the arithmetic equation in Chapter 9 are the addition and subtraction of integers. The need for subtraction also promotes the introduction of negative integers. The subtraction operation can be regarded as solving the equation A+X = B. If both A a+x=b are natural numbers, then the given equation may not have a natural number solution. In order to make it always have a solution, it is necessary to expand the natural number system into an integer system. Prime numbers are also called prime numbers. Refers to a natural number greater than 1, except 1 and the integer itself, which cannot be divisible by other natural numbers. In other words, a natural number with only two positive factors (1 and itself) is a prime number. Numbers greater than 1 but not prime numbers are called composite numbers. 1 and 0 are neither prime numbers nor composite numbers. Prime numbers play an important role in number theory. Odd number: In an integer, the number divisible by 2 is even, and the number divisible by 2 is odd. Real numbers include rational numbers and irrational numbers. Among them, irrational number is infinite acyclic decimal, and rational number includes integer and fraction.