The only issue I had was that it wasn't immediately clear whether the shift should increase by 1 every character (e.g. n+2 if shift is 2) or by the shift value for every character (e.g. 2n if shift is 2). The answer is that it should increase by 1 every character (n+2 if shift is 2) - which was the first option I tried.

Just so you know, in some non-integer bases (for example base pi), there are multiple possible representations for the same actual number.

For example, in base pi you could write "0.33" but this is actually greater than 1.