My diaries often close with a "Math Corner," usually set up as a brainteaser. I haven't aimed for anything heavy with these puzzles, just something for a person to while away ten minutes with during a coffee break.
Some of the puzzle solutions got a web page of their own with my solution. If a puzzle didn't get a page of its own, that was because either (a) I thought it was too easy to be worth putting up a page for, or (b) I forgot. For cases covered by (a), there would be be an appropriate note in the following month's diary. For the (b) cases, I am sorry.
[Added September 2014 : I shall very occasionally include a brainteaser in a column at some other outlet. If it justifies a worked solution, I'll post it here.]