Well, top -n 3 works for me (Mandriva Linux release 2010.2 (Official) for x86_64
Kernel 188.8.131.52-desktop-2mnb on a Dual-processor x86_64 / \l) but it seems that there are different versions of top, because online manuals don't have the same interpretation of -n as my manual. I have
-n : Number of iterations limit as: -n number
Specifies the maximum number of iterations, or frames, top
should produce before ending.