Does it need to be in that specific format/order or are you simply looking for shortened numbers? There's a custom function on briandunning.com called BaseConvert that I use to transform a numeric serial number to Base 36. So record "217161" becomes "4NK9". I still have a serial number field but have a second calculated field named something like "_serial36" that converts it if I need a smaller string.
What is the sequence you are aiming for that will keep working 100K records out?
Will the next sequence after 2ZZ be 3AAA, or are there going to be 1AB, or 3ABC in the works somewhere? How about 33CCC? At what point is the numeric vs the alpha pieces in the sequence updated?
Once your long-term sequence is clear, you could script the numbering by checking the MAX(createdTimeStamp field), capture the number in that record and then test to determine the next to assign. Admittedly, this could get tricky in a multi-user system if lots of new records are added regularly or by importing. It would be safer to establish a alternate-base system which could simply assign numbers in numeric sequence using the base coding.
Does anyone know how to number records like this?
Record 1A, 1B, 1C.....1Z, 1AA, 2AA etc
What numeric base are you trying to describe?