What is the proper formula for a geometric sequence

Geometric sequences work according to the simple rule of multiplying a constant number of one term to get to another number they are called geometric sequences.

Example:

1, 2, 4, 8, 16, 32, 64, 128, 256, ... This geometric sequence is an example that shows a factor of 2 between each number. So each term besides the first term will be found by multiplying the previous term by 2.