> I've got a hard time imagining they were going for a solution other than you adjusting the base.
I agree that this is probably what they were going for, but it still seems a bit ridiculous that the conversion from numbers to the chosen representation is not subject to the same rules (i.e., you can call `.toString(15)`, and this definitely uses numbers under the hood!). If this is allowed, then you could also encode your numbers as the string "{n % 3}{n % 5}" and be done with it. Or if they wanted a unique encoding, "{n}{n % 3}{n % 5}" would work too!
I agree that this is probably what they were going for, but it still seems a bit ridiculous that the conversion from numbers to the chosen representation is not subject to the same rules (i.e., you can call `.toString(15)`, and this definitely uses numbers under the hood!). If this is allowed, then you could also encode your numbers as the string "{n % 3}{n % 5}" and be done with it. Or if they wanted a unique encoding, "{n}{n % 3}{n % 5}" would work too!