## Arithmatical - Numbers

Important Facts and Formulae

1. |
Counting numbers 1, 2, 3, 4, 5, .. are called |
---|

2. |
All counting numbers together with zero form the set of I. 0 is the only whole number which is not a natural number. II. Every natural number is a whole number. |
---|

3. |
I. ( 1 + 2 + 3 + .....+ n) = n (n + 1 ) / 2 II. (1 III. (1 |
---|

4. |
Even Numbers : A number divisible by 2 is called an even number. e.g. 2, 4, 6, 8, 10, etc. |
---|

5. |
Odd Numbers : A number not divisible by 2 is called an odd number. e.g. 1, 3, 5, 7, 9, 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. |
---|

7. |
Composite Numbers : Numbers greater than 1 which are not prime, are known as composite numbers. e.g. 4, 6, 8, 9, 10, 12. |
---|