Yes, and I would because if I don't know then that's my only option (short of sitting there and going "no can do"). However, given their phrasing "basic shit like factorial or fibonacci" I got the vibe this is supposed to be known by the candidate and they'd judge the candidate negatively (before having written a single line) for needing to ask
I'd assume that the purpose of a simple question like that is to test basic programming skills (can you write a loop?). Testing knowledge of a specific math concept is doesn't really fit into this goal, so you're unlikely to be penalized for it.
