## Number System

**Natural numbers ****{N}**

The counting numbers {1, 2, 3, 4, 5…} are called natural numbers;

**Whole numbers**

Natural numbers including 0 {0, 1, 2, 3, 4, 5…} are also called **whole numbers**.

Negative numbers are not considered “whole numbers.”

**Integers ****{Z}**

Positive and negative counting numbers, as well as zero: {…, −3, −2, −1, 0, 1, 2, 3, …} are called integers.

**Even Number**

The Numbers that are divisible by 2 are known as Even Numbers.

Even Numbers – 2,4,6,8,10,12,14,16,18 and so on.

**Odd Numbers**

The Numbers which are not divisible by 2 are known as Odd Numbers. In other words, the odd numbers are those numbers which are not even.

Odd Numbers – 1, 3, 5, 7, 9, 11, 13, 15, 17 and so on.

**Prime Number**

The numbers that are divisible by one and itself and not divisible by any other number.

Prime Numbers are: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29 and so on.

**Rational Number**

Any number which can be expressed in the form of, where a and b both are integers and, **b is not equal to 0** is a rational number. Ex – 3/5, 2/6. 9/8.

**Composite Numbers**

A composite number is a whole number (greater than 1) that is not prime.

Composite numbers C= (4,6,8,9 ……..,etc.)

### Number System

- Every number, which is either rational or irrational is called a real number.
- Each natural number is a real number.
- Each whole number is a real number.
- Each integer is a real number.
- Each rational number is a real number.
- Each irrational number is a real number, etc.