>I'm going to give that a try. I like this approach, as defining the gaps is my desired result. Unfortunately, this is the smallest of 8 tables that I need to look at.
>
>>Hmm, too bad. I never had to run it on more than about 40K records and worked fine there. Could you process the main file in smaller chunks?

Maybe this would work better, plain old xbase style code:

CREATE CURSOR gaps (gapstart i, gapend i)
SELECT sequence
GO TOP
nstart = nval - 1
nend = nstart
SCAN ALL
  IF nstart+1=nval
    nstart = nval
    LOOP
  ENDIF
  IF nstart<nval
    nstart = nstart + 1
    nend = nval - 1
  ENDIF
  INSERT INTO gaps VALUES (nstart,nend)
  nstart = nval
ENDSCAN

40K records takes about .08 seconds.
400K takes about .67 seconds.