I am not terribly good at maths. But recreational mathematics as a concept appeals greatly to my sense of ... I don't know, something. And it is not just that the Doctor lamented its rarity. I even bought a book about it from the 50s, once. I didn't understand most of it.

Anyway, here is a New Scientist article on it. An excerpt:

Gary Foshee, a collector and designer of puzzles from Issaquah near Seattle walked to the lectern to present his talk. It consisted of the following three sentences: "I have two children. One is a boy born on a Tuesday. What is the probability I have two boys?"

The event was the Gathering for Gardner earlier this year, a convention held every two years in Atlanta, Georgia, uniting mathematicians, magicians and puzzle enthusiasts. The audience was silent as they pondered the question.

"The first thing you think is 'What has Tuesday got to do with it?'" said Foshee, deadpan. "Well, it has everything to do with it." And then he stepped down from the stage.