# 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†’ 12, 22, 32, 42â€¦
Series (ii) is â†’ 12 + 1, 22 + 2, 32 + 3, 42 + 4â€¦

With this, any term or in general t
n, for either of the two series can be very easily found out.
For series (i), t10 = 102
For series (i), t10 = 102 + 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:
1. Arithmetic Progression
2. Geometric Progression
3. Harmonic Progression