A geometric sequence (also known as a geometric progression) is a sequence of numbers in which the ratio of consecutive terms is always the same.
For example, in the geometric sequence 22, 66, 18, 54, 162, …, the ratio is always 33. This is called the common ratio.
If the first term of the sequence is aa and the common ratio is rr, then the geometric sequence can be written as
a, ar, ar2, ar3, …, arn−1, …a, ar, ar2, ar3, …, arn−1, …
which has nth term arn−1