Arithmatical - Numbers

CATEGORY

Important Facts and Formulae
1.

Natural Numbers :

Counting numbers 1, 2, 3, 4, 5, .. are called natural numbers.
2.

Whole Numbers :

All counting numbers together with zero form the set of whole numbers. Thus,

I. 0 is the only whole number which is not a natural number.

II. Every natural number is a whole number.
3.

Some Important Formulae :

I. ( 1 + 2 + 3 + .....+ n) = n (n + 1 ) / 2

II. (1 2 + 22 + 32 + ..... + n2) = n ( n + 1 ) (2n + 1) / 6

III. (1 3 + 23 + 33 + ..... + n3) = n2 (n + 1)2 / 4

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.