Flexagons and the Math Behind Twisted Paper

This is a good introduction to flexagons, I suppose.
It's quite easy to follow through, and it introduces very interesting concepts which one couldn't have imagined at first, like Möbius strips, magic squares and Catalan numbers.
For the most part, it's a hands-on course in which you'll have to print and cut the templates for the flexagons, and play with them a little bit in order to get confident with the flexes and going through the different faces of the flexagon.
But as I said, there are very interesting concepts too related with the flexagons.
If you're interested in recreational maths or in spending some time learning new things and having some fun, this is a good course.
I took it because I had some time left till the beginning of the University course and because it looked like an easy-to-follow and entertaining course, and it turned out to be so.
The only con I find is the limited access to the course that FutureLearn offers, but it's still enough to finish it.