I can kinda vaguely see how that might be producing the right answer, but it still feels like a most extraordinary cheat to me.
Exactly! When I first saw it I thought that cannot possibly work, but checking it it does. My next thought was "Why have I never seen this before, is it just me, has everybody else been using this equation for years?".
Zeller's Congruence and the Ordinal Date code are making my head hurt even more, but I'll try and work through them -thanks.
I would still be interested if people have or have not seen the formula before. Is it a little gem that has been lying lost in cyberspace or is it really quite well know?