# Number Series Tricks, Questions and Videos

**Number Series Important Questions - Page 6**

** Number Series Video Lecture - Page 7**

**PRIME NUMBERS** : A prime number is a a counting number greater then 1, which is divisible only by 1 and by itself. For example: 2, 3, 5, 7, 11, etc.

**PERFECT SQUARE** : A whole number whose square root is also a whole number is called a perfect square. For example: 4, 9, 16, etc.

**PERFECT CUBE** : A whole number whose cube root is also a whole number is called a perfect cube. For example: 1, 8, 27, 64, etc.

## Arithmetic Progression (AP)/ Arithmetic Series

An arithmetic progression is the sequence of numbers in which a number in the series is obtained by adding a constant number to the previous number in the series.

The sum of first n terms of the series s=n2{2a+(n−1)d}

Where a is the first term and d is the common difference.

The sum of the series (of all n terms)

= n2{a+l}=n2{2a+(n−1)d}

Where ‘a’ is the first term and ‘l’ is the last term

**For example,**

2, 5, 8, 11 ……. n common difference = 3

9, 15, 21, 27………. n common difference = 6