Formula for smallest possible positive value with given decimal places count

Question

There is a project I'm working on which gives me a decimal places count for values which I have to work with. Now I need to calculate the smallest possible positive value with the mentioned count of decimal places.

For example:

I need a formula which maps 5 to 0.00001, maps 3 to 0.001, and maps 10 to 0.0000000001.

Any idea how I could achieve this?

Please excuse my English.

Answer 1

Maybe the following is what you want: $$j\mapsto 10^{-j}$$ For $3$ this would be $10^{-3}=0.001$.