If you go around a loop on a curved surface, you come back rotated - this effect is called “holonomy”. The green piece cannot rotate in place; you must use holonomy to dodge its arms around the pegs blocking its way and escape the maze!
Full video: youtu.be/LG5HUd0hzzo

Just in time for , a new 3D printed puzzle. Use the 4th (dimension) to solve it!
Video: youtu.be/LG5HUd0hzzo

Mathemalchemy: a collaboration between 24 mathematicians and mathematical artists, to create an installation celebrating the beauty and creativity of mathematics. Video: youtu.be/8QQywzbGAU8 More details at mathemalchemy.org

Why the 14-15 puzzle is impossible, and how to solve it anyway. youtu.be/7WWcbBwvG40

If you’d like a little negative curvature with your classic sliding-tile brainteaser: introducing the 15+4 puzzle. YouTube video: youtu.be/Hc3yfuXiWe0

Call for papers on "The Art of Mathematical Illustration"! Edmund Harriss and I are guest editors for this special issue of The Journal of Mathematics and the Arts. The deadline for submissions is June 1st 2021. think.taylorandfrancis.com/spe

You, a tech startup with millions in angel finance: made an app to turn handwritten maths into TeX.

Me, just the worst kind of smart alec: convinced a pen to turn TeX into handwritten maths

For some reason, I just like watching Lloyd's algorithm (en.wikipedia.org/wiki/Lloyd%27) in animated form.

This sculpture (designed by Chaim Goodman-Strauss) has something to do with it!

Sneak peek of a new project.

My latest puzzle (a belated Christmas present to myself) is the Hanayama Twist. I'm very pleased with it: an elegant symmetric two-piece design, solid feel in the hand, and a solution that is surprisingly complicated but not tediously long. My only complaint is that the solution is very linear, with almost no ways to go wrong if you keep moving on from things you've already done. Anyway here's a map I drew to help me, also used as an example of an implicit graph in my graph algorithms lectures.

Stereographic projection grid.

This is your brain on hyperbolic geometry.

Stained glass rectangular toroid Borromean rings: accomplished.

A paper-craft model of a chunk of the gyroid, a triply periodic minimal surface.

Think of a number, and keep a running total starting at 0. Each turn, add your number on to the total. Then, if the old total was a multiple of your number, add one to your number. Otherwise, subtract 1.
The game ends when your number is 1.

Which starting numbers eventually get to 1? In the video, it looks like starting at 4 doesn't, but starting at 2 does.

My new sequence, oeis.org/A338807, lists the numbers that eventually reach 1. I'd love to know if there's a pattern!

Complete classification of tetrahedra whose angles are all rational multoples of $$\pi$$: threadreaderapp.com/thread/133, via aperiodical.com/2020/12/aperio

The original paper is "Space vectors forming rational angles", arxiv.org/abs/2011.14232, by Kiran S. Kedlaya, Alexander Kolpakov, Bjorn Poonen, and Michael Rubinstein

I've got a new sequence in the OEIS. It's to do with a really simple number game I made up. Here's a video explaining the rules