# Different type of numbers

• Natural Number (N): it is the set of counting numbers i.e. {1, 2, 3…..}
• Whole Number (W): It is the set of counting numbers including zero in the Natural numbers.
i.e. {0, 1, 2, 3….}
• Integer (Z): It is the set of natural numbers with zero and negative natural numbers. i.e. {….-3, -2, -1, 0, 1, 2, 3…}
• Rational Number (Q): The numbers which can be represented in the form p/q where p, q are integers and q ≠ 0
Ex: 1/2, 3/4, 1/2…
• Irrational Numbers: The numbers which are not rational. These numbers cannot be written as simple fraction.
Ex: π, √2 ,√3 …
• Real Number (R): The set of numbers which includes both rational and irrational numbers.
Real numbers = Rational number + Irrational numbers + Whole numbers.
It can be positive, negative or zero.
• Prime Number: It is number which have no factor other than itself and unity.
Ex: 2, 3, 5, 7, 11, 13….
Note: 2 is the only even number which is prime.
• Composite Number: The numbers which are not prime are called composite numbers.
Ex: 4, 6, 8, 9, 10…
• Perfect Number: It is a number which is equal to the sum of all of its divisors excluding itself.
Ex: 6 = 1 + 2 + 3
28 = 1 + 2 + 4 + 7 + 14
• Absolute value of number: It is denoted by |x|
|x| = x if x is positive
= -x if x is negative
Note: |x| is always positive.
Ex: |-6| = 6, |20| = 20 etc.