James Propp

Learn how a stupid question led to an interesting, albeit spectacularly useless, way to estimate pi by tossing a coin many, many times, in this month's Mathematical Enchantments essay, "In Praise of Stupid Questions". mathenchant.wordpress.com/2026/03/12/in-…

Hexagons in Harvard Square, #6. Who knows where I took this photo?

Writing in The New Yorker earlier this month, Stephen Witt said matrix multiplication is ugly. Is he right? Check out my take at mathenchant.wordpress.com/2025/11/21/is-…

This just opened near me, and not a moment too soon. I really could use a few extra terabytes of RAM between my ears.

It’s used by X-ray technicians to take an X-ray that shows your fingers individually from the side, as you rest your hand on it with your fingers splayed. I doubt that this polytope has been studied, but it is definitely chiral in both the mathematical and etymology senses.

It’s made of spongy material and costs around $15.

Riddle: what is this object used for?

This month in Mathematical Enchantments: An 87-year-old fractal wanted to be seen and understood. I figured it could use some help. mathenchant.wordpress.com/2025/10/18/pic…

A triple negative in the headlines today: “Court lifts immigration stop limits”

@mathillustrated Come to a MOVES conference or a Gathering 4 Gardner conference or some other event I’m attending!

@JimPropp How can I buy you a coffee?

Have you ever seen balls ricochet down a network and land in bins to create not the usual bell-shaped curve but a curve with two humps or more? Soon you'll be able to at MoMath. mathenchant.wordpress.com/2025/08/23/ran…

What? No “Decolonize Catan” bumper stickers for sale? Shame on you, Internet!

I’m disappointed to learn that “hypergamy” refers to nothing more interesting than what used to be called “gold-digging”. I was hoping it referred to something more genuinely mind-bending, like being married to uncountably many people along uncountably many timelines.

I just found a few at en.m.wikiquote.org/wiki/Last_word… but that list is far from complete.

There’s a pattern in the original Star Trek series: when a bad character is vanquished, they die or leave repeating some phrase over and over (the friendly angel, Apollo, Tralayne, Charlie X, Nomad, Redjac, …). Has anyone catalogued them, because that’s what the Internet is for?

I want to support public media in underserved areas of the U.S. Is there a fund that will spend my donation where it will do the most good? nytimes.com/2025/07/16/opi…

Learn about the world of q-deformed numbers, in which 1.1 (aka 11/10), 1.01, 1.001, ... converge to 1 but .9, .99, .999, ... converge to 1's "evil twin", in my latest Mathematical Enchantments essay: mathenchant.wordpress.com/2025/07/17/whe…

Bought one. Couldn’t finish it.

"Remembering Kelly" recounts two stories I heard from David C. Kelly, who unfortunately passed away last week. mathenchant.wordpress.com/2025/06/17/rem…

George Hart informs me that this shape was first described by Alan Holden. For background, see: archive.bridgesmathart.org/2005/bridges20…

My wife asked me whether this object (the Toysmith Flashing Neutron Multi-Sensory Ball) is random or has interesting mathematical properties. Do any of you know? It seems to be some sort of weaving together of nonconvex decagons.