Only a small fraction of math has practical applications, the majority of math exists for no reason other than thinking about it is fun. Even things with applications had sometimes been invented before those applications were known. So in a sense most math is designed to be fun. Of course it's not fun for everyone, just for a special class of people who are into this kind of thing. That makes it different from Angry Birds. But there are many games which are also only enjoyed by a specific audience, so maybe the difference is not that fundamental. A large p... (read more)