The answer is not quiet as simple as that.
You can have far more clients associated than is recommended.
It will also depend on what authentication you use but even in the worse case it is much more than you should ever consider on one AP
The design guides recommend between 15 and 30 depending on trafic profiles, this is not a limitation of the AP but rather the fact that 802.11 networks are a half duplex shared media a lot like a HUB (not a switch) If you start to go above these recomendations then network throughput and reliability will suffer
The theroectical limit is 2047 clients per AP but worst case with authentication 250 clients per AP but throughput will be no existant with this number of clients
