Some of the most satisfying number puzzles require little mathematical know-how. In fact, cracking the one below calls for thinking that is quite nonmathematical. I don’t know where or when I first ...

A number sequence has gone viral on the internet this week, reading: 2, 6, 12, 20, 30, ?. At first glance, it looks easy, but once people start solving it, they realize spotting the pattern is not so ...