Pinned toot

Hallo, new Mastodon users! Here on mathstodon.xyz we've got a couple of mathematical emoji: and . I'd love to add some more. If you can make a PNG image the same size as those, send it to me and I'll add it. Faces of famous mathematicians are an easy place to start; could we have some shapes, polyhedra, or other mathographics too?

It's the universal non-palindrome day! This is the only date consisting of nothing but zeroes and twos that is not a palindrome no matter how you write it!

02202020
20022020
20200220
20202002

Relish it, we won't have another one of these for 20,000 years

A: dns record
AA: battery
AAA: battery
AAAA: dns record

You can see that transformation in motion at squiangle.glitch.me/

121. HEADS OR TAILS. Crooks, an inveterate gambler, at Goodwood recently said to a friend,
"I'll bet you half the money in my pocket on the toss of a coin--heads I win, tails I lose." The coin was tossed and the money handed over. He repeated the offer again and again, each time betting half the money then in his possession. We are not told how long the game went on, or how many times the coin was tossed, but this we know, that the number of (1/2)

New on display in the Newcastle maths, stats and physics lobby. Based on my 'squiangle' triangle → square transformation.
This piece shows the sequence of moves triangle → square → 90° rotation → triangle → 120° rotation

I love the mastodon image captioning feature because there are a lot of good uses even for sighted users

- when federation / the other instance / your router fails & the image won't load

- explaining visual jokes while "keeping the medium intact"

- naming a visual symbol you /think/ people will know about but maybe not, so they can look it up & read more about it

- noting 'what to look for' when it's unclear

- translating an image in another language while still letting it speak for itself

And yet a Pole has never held the swede vault world record. Really makes you think.

Here's the same thing for a 2×2 grid. The triangle in the middle has to go one way or the other, so you have to break the vertical line of symmetry

I've been thinking about the fact that an n×n square grid has as many cells as a triangular lattice with n triangles on each side.
Is there a nice continuous bijection between them? When n is odd, you can at least keep one line of symmetry throughout.

I'm not sure I've seen this puzzle before, and I really like it:

We have n keys and n boxes. Each key fits only one box. We shuffle the keys and put one in each box. Then we randomly break open 1≤k≤n boxes. What is the probability that we can unlock all the other boxes?

John von Neumann
Werner Boy

Girl???

accessibility, color contrast

A silly fact: 987654312/123456789 = 8

Are you kidding.

Also, bold ploy by someone in MS to recommend Chrome over their own browser.

ah yes, the classic proof

Currently embroiled in an all-Chris email conversation. Have had to resort to using surnames to have any chance of knowing who we're talking about

Consider the algorithm "M(x): if x<0 return -x, else return M(x-M(x-1))/2". This algorithm terminates for all real x, though this is not so easy to prove. In fact, Peano Arithmetic cannot prove the statement "M(x) terminates for all natural x". Paper to come! Joint work with @jeffgerickson and @alreadydone

Came across the fact that $\frac{1}{96} = \sum_{k=1}^{\infty} \frac{k^2}{(k+1)(k+2)(k+3)(k+4)(k+5)}$, without any references.
How do I go about proving that? I hope the answer doesn't involve the Riemann ζ function.

This season’s must-have accessory ✨🐓

A Mastodon instance for maths people. The kind of people who make $$\pi z^2 \times a$$ jokes. Use $$ and $$ for inline LaTeX, and $ and $ for display mode.