Video: youtu.be/LG5HUd0hzzo

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

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 #plotter to turn TeX into handwritten maths

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

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.

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, https://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 \(\pi\): https://threadreaderapp.com/thread/1333670741590503425.html, via https://aperiodical.com/2020/12/aperiodical-news-roundup-november-2020/

The original paper is "Space vectors forming rational angles", https://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

https://www.youtube.com/watch?v=ZtGcd0xxqac

Full video at https://youtu.be/ljyJFsaAE84.

Mathematician working mostly in three-dimensional geometry and topology, and mathematical artist working mostly in 3D printing and virtual reality.

Joined Apr 2017