NUMBER SYSTEM

The ten symbols 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 are called digits, which can represent any number

Natural Numbers: These are the numbers (1, 2, 3,etc.) that are used for counting. It is denoted by N.

There are infinite natural numbers and the smallest natural number is one (1)
Even numbers: Natural numbers which are divisible by 2 are even numbers. It is denoted by E.
E = 2, 4, 6, 8, ….
Smallest even number is 2. There is no largest even number.
Odd numbers: Natural numbers which are not divisible by 2 are odd numbers.
It is denoted by O.
O = 1, 3, 5, 7, ….
Smallest odd number is 1.
There is no largest odd number.

Based on divisibility, there could be two types of natural numbers:

Prime and Composite.
a) Prime Numbers: Natural numbers which have exactly two factors, i.e., 1 and the number
itself are called prime numbers. The lowest prime number is 2. 2 is also the only even
prime number.
b) Composite Numbers: It is a natural number that has atleast one divisor different from unity
and itself.
Every composite number can be factorized into its prime factors.
For example: 24 = 2 × 2 × 2 × 3. Hence, 24 is a composite number.
The smallest composite number is 4.
Whole Numbers: The natural numbers along with zero (0), from the system of whole numbers.
It is denoted by W.

There is no largest whole number and
The smallest whole number is 0.
Integers: The number system consisting of natural numbers, their negative and zero is called integers.
It is denoted by Z or I.
The smallest and the largest integers cannot be determined.

• 1 is neither prime nor composite
• 1 is an odd integer.
• 0 is neither positive nor negative.
• 0 is an even integer.
• 2 is prime & even both.
• All prime numbers (except 2) are odd.

The number line: The number line is a straight line between negative infinity on the left to positive infinity
on the right.