I was going to say that about n; it is not the same as casting out: the digits always add, at least in base ten -- he didn't elaborate -- to a multiple of three; so that you can tell if the number is a multiple ... so, I guess, you could "cast out some threes to get 0, 1 or 2 (of course, you can stop at 12, 60, 62 etc.
> You might want to re-read. The general case is that, in base "n", > > casting out "n-1" works. This is true, not just in base 10, where > > 9 is the square of a prime, but in all bases. For instance, in > > octal, one casts out 7s. > > > > -- > > Michael F. Stemper > > If you take cranberries and stew them like applesauce they taste much > > more like prunes than rhubarb does.