Fixed, thanks to you and @Katzen_gott

Thanks, merged

Glad you enjoyed it!

Thanks, I've changed it now

I like this one a lot! How did you come up with the formula for the exponent?

Thanks, I've incorporated these changes!

Thanks!

That's a valid point. I think this problem may be a fun one to think about iteratively/recursively though, so I'd like to accept non-constant-time solutions.

Slick!

The reference implementation returns -2 for those inputs. This contradicts the kata description, which claims

Input will always be a non-negative integer

and

If input data is invalid you should return 0