I just went through a binge of watching nearly Apollo mission-related program I could get my hands on (yes, this included Fox’s execrable Did we go to the moon? travesty of an hour’s wasting of my life). I watched the incredibly, complete HBO From the Earth to the Moon 12-part series, the awesome Criterion DVD of For All Mankind, and even Opie Howard’s Apollo 13 for the second time.
But, nowhere in there, at least as far as I know, did I get an explanation of why there were no Apollo missions 2, 3, 4, 5, or 6. I did some searching and found this page, which explains that 4-6 were unmanned missions, and that Apollo 7 was the first crewed Apollo flight. (Apollo 1, of course, was the tragic launchpad fire on 27 January 1967.)
So, what were Apollos 2 and 3?