How to calculate exponentially in Roll20?

I am working on a character sheet that uses exponential multiplication, but everything I try in my formulas does not seem to work. Effectively there is a Stat, and every time it goes up, it's effect doubles (from it's previous level). E ffectively if the stat is 2, I'd want it to multiply by 2. 3, by 4. 4, by 8. 5, by 16. And so on. Is there a function in Roll20 that allows for this?

Preface: I am not a character sheet coder. The following is general information. In Roll20 exponents are 2**2 instead of 2^2.  If the exponent is changing over time you'll need a way to store the previous exponent in order to calculate the next one. 

That looks like it's just 2**(myVariable - 1) or, if it's a roll button 2**(@{myStat} - 1) ...unless there's more to it than the example given?

Ah, thank you so much! I figured I was missing something there, and that'd be it. Very appreciated.