See this question:
https://stackoverflow.com/questions/16447693/how-many-trees-are-possible
This is a question from the ongoing CodeChef contest. The OP should not ask about it here. However, there is no valid way to stop him/her.
Although this question in itself is good, it is a form of cheating. Should we stop this behavior somehow?
Note: this question in itself is not that bad; it got +3 before I pointed out that it is from a contest.
There are also other questions like this, so it is becoming a trend:
Is Stack Overflow the new cheating panel for these contests / homeworks / etc.?
Edit Okay, I probably got a bit too excited. Anyway, it is nice to know people cares about it, and the original questions got took care of. Guess I'll be looking out for such questions in the future:)
EDIT Another one: https://stackoverflow.com/questions/16469430/no-of-trees-possible-with-n-nodes-given-some-conditions