Given the geometric sequence where a1 = 2 and the common ratio is 4, what is the domain for n?

The general term is  (a sub n; n is a subscript)

The first term is a1
The second term is a2
The third term is a3
and so on...

The first term starts at n = 1. We replace the n in  with 1 to get . A similar thing happens with n = 2 and onward

The domain is therefore the set {1, 2, 3, 4, 5, ...} which is the set of...
* Counting numbers
* Positive Whole numbers
* Natural numbers
Those are three ways to express the same set

We can also say  where n is an integer or whole number
A similar inequality would be  which is effectively the same as idea as the last inequality (n is also an integer or whole number).