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No, I can't. The answer I posted goes in a completely different direction, but of course it's quite stupid. If you know and are able to prove that these numbers indeed must be divisible by 10, then you're solving it in a smarter way, congrats!
Okay, I was wrong -- it's not obvious in Cech cohomology, at least as it's normally defined. The references though are any homological algebra course, post a different question about "what are the references" and you'll get lots of advice.
