Finding the$n^{\text{th}}$Term of a Sequence

Example 1:

In the sequence$2,6,18,54,\mathrm{...}$the first term is
$a_1=2$, the second term is$a_2=6$and so forth.

A term is multiplied by$3$to get the next term.

Example 2:

$a_n=n^2$

First term:$a_1=1^2=1$

Second term:$a_2=2^2=4$

Fifteenth term:$a_{15}={15}^2=225$