If you're only visiting for 21 days and have a Schengen visa (i.e. a 90 day tourist visa) then, no, you don't need to apply for a residence permit (and in fact will not be allowed to apply for a residence permit).
Oh, and on a Schengen visa, you aren't supposed to be working in the EU.
Cheers,
Bev
Oh, and on a Schengen visa, you aren't supposed to be working in the EU.
Cheers,
Bev