We have been taught that linear functions, usually expressed in the form y=mx+b, when given a input of 0,1,2,3, etc..., you can get from one output to the next by adding some constant (in this case, 1).
But with exponential functions (which are usually expressed in the form ), instead of adding a constant, you multiply by a constant. (In this case, 2)
We can keep going, can't we?