Disruption of consecutive numbers

I do have a tab delimited file with the following format

200 46
201 67
204 89
205 98
206 89
208 890
210 23
..
...

100's of rows

I would like to output the missing consecutive number of the first column.

The expected output will be:

202
203
207
209

It would be great if I could specify the start and end numbers. Let me know the best way to do this using awk or sed.

awk 'NR==1{n=$1;next}{while($1-n++>1)print n}' file