robinhouston
@robinhouston.mathstodon.xyz.ap.brid.gy
📤 98
📥 2
📝 667
Maths etc. 🌉 bridged from ⁂
https://mathstodon.xyz/@robinhouston
, follow
@ap.brid.gy
to interact
The end of an era for category theory at Cambridge?
2 days ago
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Funny idea from
@jgrahamc
:
https://aperiodictable.com/
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Infinite Penrose Periodic Table
https://aperiodictable.com/
13 days ago
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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
17 days ago
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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.
19 days ago
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reposted by
robinhouston
Timothy Gowers
23 days ago
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 […]
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Original post on mathstodon.xyz
https://mathstodon.xyz/@wtgowers/116541479140154547
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User cachecrab on Twitter noticed that Google has a rather unusual interpretation of the query “20% of £1k”.
23 days ago
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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
24 days ago
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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.
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https://mathstodon.xyz/users/pieter/statuses/116534285031160547
24 days ago
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RE:
https://mathstodon.xyz/@tao/116477353989159599
This is a nice analogy.
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https://mathstodon.xyz/users/tao/statuses/116477353989159599
25 days ago
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reposted by
robinhouston
Christian Lawson-Perfect
25 days ago
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]
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reposted by
robinhouston
Gro-Tsen
26 days ago
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
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ENCYCLOPEDIA OF TRIANGLE CENTERS
https://faculty.evansville.edu/ck6/encyclopedia/ETC.html
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I want to know the relative popularity of the Platonic solids, but a Mathstodon poll can have at most four options.
about 1 month ago
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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.)
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https://mathstodon.xyz/users/de_Jong_Tom/statuses/116458595973450171
about 1 month ago
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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?)
about 1 month ago
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RE:
https://mathstodon.xyz/@henryseg/116437443825536011
This is now my favourite physical object.
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https://mathstodon.xyz/users/henryseg/statuses/116437443825536011
about 1 month ago
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Meet the zonohedrification of the rhombicosidodecahedron.
https://skfb.ly/pIOIO
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Zonohedrified rhombicosidodecahedron - Download Free 3D model by robinhouston
This is the zonohedrification of the rhombicosidodecahedron. It is a zonohedron with 30 zones. Each zone consists of 58 edges, so the whole polyhedron has 58 × 30 = 1740 edges. Since all its faces are quadrilateral – actually they are all rhombuses – and each edge belongs to two faces, it must have 1740 × 4 / 2 = 870 faces. Since the polyhedron clearly has Euler characteristic 2, we may compute the number of vertices as 1740 - 870 + 2 = 872. - Zonohedrified rhombicosidodecahedron - Download Free 3D model by robinhouston
https://sketchfab.com/3d-models/zonohedrified-rhombicosidodecahedron-0bc66439ab3b41779edcd2233974f7be
about 1 month ago
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Spotted in The American Mathematical Monthly, Vol. 99, No. 2 (Feb., 1992)
about 1 month ago
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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/
about 1 month ago
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I knew about the
https://en.wikipedia.org/wiki/Teapotahedron
, of course, but the
https://en.wikipedia.org/wiki/Zocchihedron
is new to me.
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Utah teapot - Wikipedia
https://en.wikipedia.org/wiki/Teapotahedron
about 1 month ago
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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 […]
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Original post on mathstodon.xyz
https://mathstodon.xyz/@robinhouston/116415356325102429
about 1 month ago
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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 […]
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Original post on mathstodon.xyz
https://mathstodon.xyz/@robinhouston/116410851408297334
about 2 months ago
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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 […]
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Original post on mathstodon.xyz
https://mathstodon.xyz/@robinhouston/116410047757257052
about 2 months ago
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RE:
https://mathstodon.xyz/@krystalguo/116408728086548168
It's rather charming that this sort of encouragement makes AlphaEvolve work better.
about 2 months ago
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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 […]
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Original post on mathstodon.xyz
https://mathstodon.xyz/@robinhouston/116405254492922325
about 2 months ago
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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
about 2 months ago
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Is math big or small?
https://chessapig.github.io/talks/Big-Small
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Is math big or small?
https://chessapig.github.io/talks/Big-Small
about 2 months ago
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I don't remember coming across the Heptagon Numbers before. Very nice!
about 2 months ago
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Did you know that there's a spherical analogue of Heron's formula? (TIL)
https://mathworld.wolfram.com/LHuiliersTheorem.html
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L'Huilier's Theorem -- from Wolfram MathWorld
Let a spherical triangle have sides of length a, b, and c, and semiperimeter s. Then the spherical excess E is given by
https://mathworld.wolfram.com/LHuiliersTheorem.html
about 2 months ago
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reposted by
robinhouston
Tom Gauld
2 months ago
My cartoon for this week’s
@newscientist.com
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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
2 months ago
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reposted by
robinhouston
Julia Evans
2 months ago
how diffie hellman key exchange works (with as little math as possible)
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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 […]
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Original post on mathstodon.xyz
https://mathstodon.xyz/@robinhouston/116280236370534389
2 months ago
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Clever.
2 months ago
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Does this really work? I wish I had known when I were younger.
2 months ago
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“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!
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Holey Squares Cube
https://puzzleworld.org/PuzzleWorld/puz/holey_squares_cube.htm
2 months ago
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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 […]
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Original post on mathstodon.xyz
https://mathstodon.xyz/@robinhouston/116240598676377805
3 months ago
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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.”
3 months ago
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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]
3 months ago
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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.
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https://mathstodon.xyz/users/liuyao/statuses/116227619091892470
3 months ago
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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
3 months ago
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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.
3 months ago
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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]
add a skeleton here at some point
3 months ago
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reposted by
robinhouston
Jos Geluk
3 months ago
@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.
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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
3 months ago
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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]
3 months ago
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Has the Mystery of Angzarr finally been solved? ⍼
https://ionathan.ch/2026/02/16/angzarr.html
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U237C 方位角
U237C Is Azimuth (ionathan.ch) 06:33 ↑ 104 HN Points
https://ionathan.ch/2026/02/16/angzarr.html
3 months ago
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An unusual polyhedron whose dihedral angles are all right angles.
https://sketchfab.com/3d-models/orthogonalized-tetrahedron-c26dd2789da3406bbb00e5df769ade6d
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Orthogonalized tetrahedron - Download Free 3D model by robinhouston
An unusual orthogonal polyhedron – i.e. a polyhedron whose dihedral angles are all right angles. - Orthogonalized tetrahedron - Download Free 3D model by robinhouston
https://sketchfab.com/3d-models/orthogonalized-tetrahedron-c26dd2789da3406bbb00e5df769ade6d
3 months ago
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New integer sequence just dropped
https://oeis.org/A392894
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A392894 - OEIS
https://oeis.org/A392894
3 months ago
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RE:
https://hachyderm.io/@ruuddotorg/116150427971106885
Ok, this is kind of cool. Can you find an elegant proof?
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https://hachyderm.io/users/ruuddotorg/statuses/116150427971106885
3 months ago
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A four-dimensional version of the classic game Lights Out, from
@nanma80
:
https://www.nan.ma/lights_out_4d/
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Lights Out 4D
A puzzle game on stereographic projections of 4D polytopes
https://www.nan.ma/lights_out_4d/
3 months ago
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