Yeah, Neumann was well into the nutty end of the genius spectrum. As in, his genius was so nuts that it's hard to believe he was real. Similar with "The strangest man to ever visit my lab" - Paul Dirac (that's a quote from Neils Bohr). At least Dirac appeared to be autistic enough from the description that I'm not surprised he was able to do what he did. It's a superior intelligence, but I'm guessing he was obsessive about shit as well.

Of course, once you know how to sum infinite geometric series it's not too hard to come across the answer that way ;)

Or swallow, if you think Wigner's account is more accurate than Halmos'.