The real ID of your DB should not have any meaning and should simply be set as a field with auto enter serial value.
The serial "thing" that you need can be obtained using the "Replace Field Contents" menu or Script Step.
Remember to do that command on a copy of your DB because that command isn't undoable.
Raybaudi - thanks. Not clear on how to enter the serial values retrospectively in an existing file of x thousand records. If I'm following you, you advise auto-entering the sequential srial value, then replacing it with the calculation I need. BUT - how do I get the serial values entered in twenty thousand records? Gracias.
Thanks. Problem solved: created clone of file, instructing auto-entry of calculated ID, and imported all records into clone, which worked smoothly.