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Natural Numbers :

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

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.

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