From the command line do
dir /b > filelist.csv
Then open that file in excel. Sort the data by that column so the numbers go in order. Using find and mid/left/right extract the number into the B column. Maybe something like =VALUE(MID(A1,5,4)) . Then use the following formula in the C column:
=IF(B2-B1>1,B2-B1-1,"")
If the number skips, then it'll print the number of files missing in this instance. It'll print nothing if the files don't skip.[DOUBLEPOST=1389632283,1389631755][/DOUBLEPOST]There's probably a more elegant way to extract just the missing numbers from this, but since it's probably a one-off job I'd just continue on with easy stuff.
Go ahead and change column C to a simpler =B2-B1-1, then in column D do:
=IF(C2>0,B1+1,"")
In column E do:
=IF(C2>1,B1+2,"")
This will return the missing files if you have runs up to 2 in a row missing. You'll have to continue the pattern in F, G, H, and so forth if you find you have runs of numbers much longer.