An algorithm for converting a base-10 number to a base-N number

Question

I am looking for a way to convert a base-10 number into a base-N number where N can be large. Specifically i am looking at converting to base-85 and back again. Does anyone

Answer 1

Fixnum#to_s won't help you, as it only goes up to base 36.

I'm surprised that you're going up to base 85. Can you explain how radixs work?