Today is Hexaflexagon Day - around the world math enthusiasts are celebrating birthday of Martin Gardner. You can see and listen Martin Gardner on Nature of Things. or read an interview with Martin Gardner. Of course, I cannot believe if you are reading this blog and have not joined those many millions on YouTube who has become fans of hexaflexagons watching Vi Hart's videos on hexaflexagons.
My first introduction into "recreational mathematics" was in 1966 when I as a sixth grader won my first math olympiad. My teacher gave me a little book by Martin Gardner. It was translation in Latvian of Martin Gardner's 1956 book:
Martin Gardner is certainly responsible that I always tried to make math visual and tangible.
So my tribute for Martin Gardner's birthday is this online exhibit.
The following paintings are all having something in common. Can you figure out what it is?
If so far you have not figure it out - here is a clue: