I suspect I'm going to have to write a utility to do this for me but there *might* be something to do it for me.
I want to spot files missing from a sequence, e.g. if I see:-
dscf1253.jpg dscf1254.jpg dscf1256.jpg dscf1257.jpg dscf1258.jpg dscf1259.jpg
I want to be told that dscf1255.jpg is missing.