1. Natural Numbers: Counting numbers I, 2. 3, 4, 5,….. Are called natural artillery.

2. Whole Numbers: All counting numbers together with zero form the set of whole number. Thus,

(A) 0 is the only whole number which is not a natural number.

(B) Every natural number is a whole number

3. Integers: All natural numbers. 0 and negatives of counting numbers ie., – 3, – 2, – 1. 0.

I. 2, 3…… Together form the set of integers

(A) Positive Integers t 11. 2. 3, 4 …I is the set of all positive integers.

(B) Negative Integers: (- I, – 2, – 3……I is the set of all negative integers.

(C) Non-Positive and Non-Negative integers: 0 is neither positive nor negative.

So, 0, 1, 2, 3. ….. I represents the set of non-negative integers, while (0, – I, – 2, – 3,)

Represents the set of non-positive integers.

4. Even Numbers: A number divisible by 2 is called an over, number. e.g.. 2. 4. 6, 8. 10. Etc.

5. Odd Numbers: A number not divisible by 2 is called an odd number. es, 1. 3. 5, 7, 9, 11, etc.

6. Prime Numbers: A number greater than 1 is called a prime number, if it has exactly Two factors namely 1 and the number itself.

Prime lumbers upto 100 are. 2, 3, 5, 7. II, 13. 17. 19. 23. 29. 31, 37. 41, 43, 47, 53, 59, 81, 87, 71. 73, 79, 83, 89, 97.

7. Composite Numbers: Numbers greater than 1 which are not prime, are known OS composite numbers. eg., 4. 6. 8. 9, 10. 12.

Note: (1) 1 as neither prime nor composite.

(ii) 2 is the only even number which is prime.

(iii)There are 25 prime numbers between 1 and 100.

8. Co-primes prime numbers a and b are said to be co primes. if their H.C.F. is 1. e,g., (2, 3), (4. 5). (7, 9), (8. 11). Etc. are co-primes.