American fighter prefix

Can anybody help me with the missing numbers in American fighter designation:

F-4, F-5, F-6 (missing), F-7 (missing), F-8, F-9 (missing), F-10 (missing), F-11 (missing), F-12 (Blackbird), F-13 (missing), F-14, F-15, F-16, YF-17, F/A-18, F-19 (missing), F-20, F-21 (missing), F-22, F-23, F-24>33 (missing), F-34 and F-35.

Any explanation would help where and why are these missing aircrafts?