Export will deal with Found Set.
Find records NameLast = A
It will export only records with a name starting with A.
Exporting isn't the right solution...
You'll end with some records data, not a copy of your DB.
So for me the best way is to:
1) duplicate your DB
2) on the duplicate copy do an OMIT multiple starting from record 20
3) show omitted
4) delete the found set