The end of an era for category theory at Cambridge?

Funny idea from @jgrahamc: https://aperiodictable.com/

How many sheets of A10 paper can you fit into one sheet of A0? This video has the answer! (And the answer is probably not the first thing you thought of.) https://youtu.be/zDKBCIMkDbw

Great stuff from Neil Sloane and Numberphile! https://youtu.be/UiX4CFIiegM https://youtu.be/VgmDuBCayPw The second video is the most interesting, but you need to watch the first one first in order to understand it.

I've just written a blog post in which I describe a research-level problem (due not t Erdos but to Melvyn Nathanson) that ChatGPT 5.5 Pro recently solved. With a guest section by Isaac Rajagopal, on whose work ChatGPT built […]

User cachecrab on Twitter noticed that Google has a rather unusual interpretation of the query “20% of £1k”.

Have you ever wanted to see a twisty puzzle that represents the Mathieu group M₂₄? Man is this your lucky day! https://youtu.be/xwQ5dx4dE9g

RE: https://mathstodon.xyz/@pieter/116534285031160547 This is really fun! I wonder if it will become more common for papers to be accompanied by apps, as the barrier to app creation is lowered.

RE: https://mathstodon.xyz/@tao/116477353989159599 This is a nice analogy.

Lay down number bars 1, 2, 3, ... Put the bar as far to the left as you can, as high as you can: if you can stack on top of previous bars, then do so. The first 25 bars look like the attached image. The sequence is the lengths of the leftmost bar on each row […] [Original post on mathstodon.xyz]

It seems that I've stumbled upon a new triangle center that is not one of the >70k centers listed in Clark Kimberling's ‘Encyclopedia of Triangle Centers’. 🤯 faculty.evansville.edu/ck6/encyclop... Here is how it's defined: 🧵⤵️ •1/8

I want to know the relative popularity of the Platonic solids, but a Mathstodon poll can have at most four options.

RE: https://mathstodon.xyz/@de_Jong_Tom/116458595973450171 It's interesting and exciting to see this place start to be recognised in slightly more formal venues. (It slightly reminds me of when the internet as a whole was rather disreputable, which honestly I preferred.)

I thought Peter Selinger was on here, but I can't find him. Has he left us? Just looking at this interesting new paper https://arxiv.org/abs/2604.20964 which does cite Mathstodon posts by @pieter. (@christianp first citation of Mathstodon in a paper, or have there been others?)

RE: https://mathstodon.xyz/@henryseg/116437443825536011 This is now my favourite physical object.

Meet the zonohedrification of the rhombicosidodecahedron. https://skfb.ly/pIOIO

Spotted in The American Mathematical Monthly, Vol. 99, No. 2 (Feb., 1992)

This is rather amazing: a set of 3d-printable adapters making it possible to connect pieces from nine different construction kit toys. https://fffff.at/free-universal-construction-kit/

I knew about the https://en.wikipedia.org/wiki/Teapotahedron, of course, but the https://en.wikipedia.org/wiki/Zocchihedron is new to me.

I didn’t realise this article was out already! Featuring some computations and diagrams by me (which, to my great excitement, Don Knuth emailed me about when he heard of them). _On Max Bill’s gelbes feld_ by Barry Cipra. https://www.ams.org/journals/notices/202605/noti3334/noti3334.html I […]

There’s a fun paper showing that you can define all elementary functions using just two primitive operations: the constant 1, and the binary function eml(x, y) := e^x - log(y). https://arxiv.org/abs/2603.21852 That’s a neat little result, which makes for some fun games. What’s the simplest […]

I guess we’re all getting a little tired of talking about this sort of thing, but I think this is the most impressive example yet of an LLM-generated solution to a long-open mathematical problem: https://www.erdosproblems.com/forum/thread/1196 Jared Lichtman, a mathematician who has spent (in […]

RE: https://mathstodon.xyz/@krystalguo/116408728086548168 It's rather charming that this sort of encouragement makes AlphaEvolve work better.

Unfortunately there is no way I can persuade you to watch this by quoting a particularly amusing moment, because there are so many particularly amusing moments that I can’t possibly choose one. https://youtu.be/M1si1y5lvkk Here’s the paper, in case you’re more of a reader than a viewer […]

2025 was the first squared-triangled-squared-triangle number for 2024 years, and I spent the whole year not knowing that! https://youtu.be/aulrY8Y4VW8

Is math big or small? https://chessapig.github.io/talks/Big-Small

I don't remember coming across the Heptagon Numbers before. Very nice!

Did you know that there's a spherical analogue of Heron's formula? (TIL) https://mathworld.wolfram.com/LHuiliersTheorem.html

My cartoon for this week’s @newscientist.com

Speaking of Hoffman’s packing puzzle (as I recently was), I just found out about Oskar van Deventer’s witty mashup of Hoffman’s packing puzzle with Piet Hein’s Soma Cube: https://www.puzzlemaster.ca/browse/3dprinted/16775-hoffman-soma

how diffie hellman key exchange works (with as little math as possible)

This is mildly interesting: It looks as though current LLMs are becoming at least competitive with expert humans at solving Diophantine equations. Here a new MO contributor has used GPT 5.4 to find solutions to a couple of Diophantine equations that were posted by Bogdan Grechuk in 2023, and […]

Clever.

Does this really work? I wish I had known when I were younger.

“The puzzle in the photograph is now in the collection of HRH Prince Charles.” https://puzzleworld.org/PuzzleWorld/puz/holey_squares_cube.htm Apparently the King collects geometric puzzles!

I just stumbled across this. I haven’t tried it yet. (It’s printing now.) I had not heard about this interesting discovery! https://www.printables.com/model/221119-knuths-packing-puzzle “In 1978 Hoffman proposed that a if you take cuboids with size A×B×C, you can always pack 27 into a cube […]

The Wikipedia page ‘Union Jack’ includes an unexpected mathematical digression: “It is one of two national flags with two-fold rotational symmetry, symmetry group C₂, the other being the flag of Trinidad and Tobago.”

RE: https://mathstodon.xyz/@JosephORourke/115741946729136640 I totally missed the news of this book at the time, but I recently saw it mentioned on @chalkdustmag, and got a copy today. I've already learnt of this remarkable folding wooden table, designed by […] [Original post on mathstodon.xyz]

RE: https://mathstodon.xyz/@liuyao/116227619091892470 This (the Observable link in the quoted post) is a very nice visualisation, which complements the 3b1b video with a different perspective.

What are the chances that two different people would make videos for π day about estimating the value of π from a sequence of random bits, and that they would use COMPLETELY different methods? https://youtu.be/kahGSss6SsU https://youtu.be/WUCm18WFuCE

I don't normally like jigsaws, but when I saw this in the window of a charity shop for £2.95 I couldn't resist.

RE: https://mathstodon.xyz/@robinhouston/116210620815721477 I don't understand why this should be, but it seems possible that you can actually tile space with just this shape and the cubes, *without* the mirror image. As I say, I don't understand this yet […] [Original post on mathstodon.xyz]

@robinhouston that is, of course, a mere summary of that other Thing, the Needle Tower by Kenneth Snelson. In the garden of the Kröller-Müller Museum.

Here’s something I made yesterday afternoon, instead of doing what I had been planning to do. A pentomino tray-packing puzzle with a twist. https://makerworld.com/en/models/2512317-pentomino-tray-packing-puzzle

TIL. In April 1974, in the middle of the night, a small group of conspirators secretly installed a large tensegrity icosahedron made from discarded telephone poles on the campus of Twente University in the Netherlands. It’s still there. People call it Het […] [Original post on mathstodon.xyz]

Has the Mystery of Angzarr finally been solved? ⍼ https://ionathan.ch/2026/02/16/angzarr.html

An unusual polyhedron whose dihedral angles are all right angles. https://sketchfab.com/3d-models/orthogonalized-tetrahedron-c26dd2789da3406bbb00e5df769ade6d

New integer sequence just dropped https://oeis.org/A392894

RE: https://hachyderm.io/@ruuddotorg/116150427971106885 Ok, this is kind of cool. Can you find an elegant proof?

A four-dimensional version of the classic game Lights Out, from @nanma80: https://www.nan.ma/lights_out_4d/