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"21st century mathematics" returns in July 2026!

What do mathematicians do? How do they make new mathematical discoveries? Why does that matter for K-12 math education? If you are a math teacher and you are curious about these questions, join in on "21st century mathematics" in July! Free, online, and flexible. www.youtube.com/watch?v=5UIx...

youtube.com

YouTube video by Justin Lanier

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Program details and registration here: justinlanier.org/21st-century...

"21st century mathematics" returns in July 2026!

youtube.com

YouTube video by Justin Lanier

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Justin Lanier @jlanier.bsky.social · 19/06/2026

Thanks! Saw you signed up, looking forward to seeing you there!

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Reposted by Justin Lanier

Hi! In July I'm once again running a free online program for K-12 math teachers called "21st century mathematics". Its goal is to help teachers to connect math they teach with some math that has been discovered in the 21st century. Pass it along! Info+register: justinlanier.org/21st-century...

A 4x4 puzzle grid, indicating an example of an alternating sign matrix; an example of a configuration of 21 points that maximized the number of pairs that are a unit distance apart. These are the two mathematical themes of the 2026 program.

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Justin Lanier @jlanier.bsky.social · 19/06/2026

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Justin Lanier @jlanier.bsky.social · 17/06/2026

Something that is then fun is that these same ideas will extend to larger grids!

4 by 4, 5 by 5, and 6 by 6 grids of the counting numbers from 1 to n squared.

Justin Lanier @jlanier.bsky.social · 17/06/2026

Yeah, for sure. Something that I wasn't expecting (but makes sense algebraically, upon reflection) is that for all six of the possible ways of choosing, the sum of the three number is equal (15). Which then for me gives ideas about why the "clump towards the middle" might yield the largest product.

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Justin Lanier @jlanier.bsky.social · 17/06/2026

I’m curious about your thinking and what you expected! Happy to hear about it.

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Justin Lanier @jlanier.bsky.social · 11/06/2026

Yeah, I’d be down for that!

Justin Lanier @jlanier.bsky.social · 11/06/2026

That's probably a bigger bite than I should take, but I applaud my earlier self for his enthusiasm. 😅

Justin Lanier @jlanier.bsky.social · 11/06/2026

Ahhh, so cool! If you were interested in reading it with others in some format, I'd be down.

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Justin Lanier @jlanier.bsky.social · 03/06/2026

@nhoskee.bsky.social @triangleman.bsky.social Hi! I haven't run across any Summer of Math announcements for this summer. Any updates for this or future summers at this time? Thanks!

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Justin Lanier @jlanier.bsky.social · 21/05/2026

Yes, there will be. I'm running behind in getting it organized and announced. Hope to have everything shared by end of May. Program will run in July. Thanks for asking!

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Justin Lanier @jlanier.bsky.social · 08/05/2026

Question: but can I use sunlight during the daytime, ok?

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Justin Lanier @jlanier.bsky.social · 16/04/2026

Cool! I don’t mean to be hyperbolic, but I for sure co-sign this challenge. Looking forward to sharing with some students tomorrow! They are pre-service teachers who have been working with parametric equations. Will let you know if any of them take it up.

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Reposted by Justin Lanier

Christopher Danielson @triangleman.bsky.social · 19/02/2026

We were invited to read from our books, which I did of course. But first I had some opening words, which I thought I'd share with you here. I'll share video too, once that's available.

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Justin Lanier @jlanier.bsky.social · 12/02/2026

My guess is that it is a play on the traditional still life, with the joke being that the TV makes the viewer in fact part of the still life; and that the rising cultural dominance of TV makes a more still life of/for us all.

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Justin Lanier @jlanier.bsky.social · 30/12/2025

Don’t You Dare Think Pentagons!

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Justin Lanier @jlanier.bsky.social · 20/11/2025

No shape is a square. Because all shapes are there. Be there or be square.

Christopher Danielson @triangleman.bsky.social · 03/11/2025

Reposted by Justin Lanier

Really nice piece on math and democracy here. (gift link) www.nytimes.com/2025/11/03/s...

nytimes.com

Moon Duchin on the ‘Mathematical Quagmire’ of Gerrymandering

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Justin Lanier @jlanier.bsky.social · 02/11/2025

If you teach Year 6 maths in the UK and you'd be willing to Zoom chat briefly with a pre-service teacher in the US for a class project, let me know? Thanks!

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Justin Lanier @jlanier.bsky.social · 31/10/2025

Very cool! Based on the registration form and what I know about other CMC-related events, am I correct in assuming that non-CA folks are welcome to attend? If so I’ll pass along to the pre-service teachers I work with! Thanks! PS enjoying the new pod eps! 👍👍👍

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Justin Lanier @jlanier.bsky.social · 28/10/2025

“The most beautiful fruit tray you can ever imagine.”

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Justin Lanier @jlanier.bsky.social · 14/10/2025

Similarly, Pennsylvania's top portion and its exclusive definition. I genuinely thought that was the point of those shapes before I recognized the shapes as state outlines. 😂

Justin Lanier @jlanier.bsky.social · 14/10/2025

Funnily enough, the top portion of Ohio might well qualify as a trapezoid by its own inclusive definition! 😄

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Justin Lanier @jlanier.bsky.social · 25/09/2025

Every bubble is popped on one side of it and raised on the other side. 😜

Justin Lanier @jlanier.bsky.social · 13/08/2025

Or—and hear me out here—give those assignments, if you think they are worth students doing, and make them a completion grade. (Or even, at times, for no grade at all.)