# Sequence and Series

Let us consider the following series:- Â•1, 4, 9, 16,â€¦
- Â•2, 6, 12, 20,â€¦

It can be observed here that each of these two series shares some or the other common property:

Series (i) is â†’ 1

^{2}, 2^{2}, 3^{2}, 4^{2}â€¦Series (ii) is â†’ 1

^{2}+ 1, 2^{2}+ 2, 3^{2}+ 3, 4^{2 }+ 4â€¦With this, any term or in general

*t*

*, for either of the two series can be very easily found out.*

_{n}For series (i),

*t*_{10}= 10^{2}For series (i),

*t*_{10}= 10^{2}+ 10.If the terms of a sequence are written under some specific conditions, then the sequence is called a

*progression*.

With respect to preparation for the CAT, we will confine ourselves only to the following standard series of progression:

- Arithmetic Progression
- Geometric Progression
- Harmonic Progression