Saddo Warning!
F-35?
I don't think so. The last fighter in the series was the YF-23, I think, the loser in the last big fighter contest. I am unaware of 24 being used, so that would logically be the next number. The X-35 was given an experimental numbe, as it is a technology "prover" first.
Although the F-117 appears to break convention, it did not really, as it's conception was during the time of the 'Century Series' (F-101, F-111 etc). Therefore, it is possible that 35 will be ditched in favour of something in the 20's.
OK, sad or what - I'll get back in me box. Before I close the lid though, whilst the X-35 looks like an attack machine, I am concercerned that the 'extra' engine will become a liability in operation, and as such, could threaten the STOVL version. We will see.