@sean tilson: it is almost certain that alias has read the comment, and so it's not clear that your answer is giving him any information that he didn't already know before he asked the question :-)
I too wondered why the question was closed. This is one of those questions that could be a triviality, an undergraduate exercise, an olympiad-level question or an unsolved problem. @alias: I think that one reason it was closed was that, although it is clearly "recreational", the OP gave no indication that he'd thought about the problem.
which I would also regard as "recreational" -- although probably Martin wouldn't -- it's "recreational" in the sense that for most people who work with schemes, this question would be regarded as rather pathological and probably not of central research interest to most (I hope I'm not opening a can of worms here!). On the other hand, what makes Martin's question a good one is that he has clearly thought about the problem and gives background information etc etc. The triangular numbers question is lazy: it just said "I saw this question on the internet -- can someone do it for me?".
@alias: if you have thought about the question for a while, then ask it yourself, and write some of the things that you tried and how they failed. It would have far less chance of being closed then.