Though we officially say you need N/2 packs for a group of N players, fan Jonathan Baker has done some technical thinking on the matter:

A: The answer depends on whether you mind pulling robot cards back out of the set-aside pile. If you trust your moderator to discretely retrieve and reuse hidden robot cards, you only need N/2 packs (rounded up) so that there’s a human card for everyone. If you want to leave all set-aside cards where they are, you need N-1 packs. This is because of the case that the suspicious humans shoot each other right down until there are only two of them left—even though the robot cards are set aside in every round (so there were never any real robots)!