Question: What would the last digit be in a base 11 system? Base 12?

I'm mostly wondering because I was thinking of a base 36 system with digits 0-9 immediately followed by the letters A-Z but I wasn't sure if that would be considered a proper numeral system, or if there was something else in place.

Answer: 
In addition to the standard A-F, etc. for hexadecimal and other systems, [this old Schoolhouse Rock](http://www.youtube.com/watch?v=BblsNzx6yEk) video (which implicitly talks about duodecimal) uses symbols that look an awful lot like the Greek chi ($\chi$) and epsilon ($\epsilon$) for ten and eleven, respectively.
IIRC, on the SWAC at UCLA in the 50's and 60's, the 6 hex digits beyond 9 were U V W X Y Z.

Also, for some reason, this pops into my mind for the hex digits: G B N J F L. These stood for "Great Big Numbers Just For Laughs".