Add New Field which auto increments/random

Is it possible to add a new field which either auto-increments as each new user registers, or which creates a unique random number? It would also be handy if it could have a some default characters before - so it would eventually look like:

ABC789556
ABC789557
ABC789558
or
ABC789556
ABC234233
ABC685234

This would be visible on the profile and admin, but not on registration and read only.

I am trying to create a membership number

Thanks

ps - any other methods of creating the something similar would be appreciated

Not possible?

a) use cbsubs to handle your membership.

b) use mySQL to create a autoincrementing field and reference to this one.

br Wolfgang

Thanks wgary

I actually found plug_cbfields, which may do something similar.

I haven't had time to look back at this problem yet.