The Aperiodical 

You're reading: Posts By Christian Lawson-Perfect

How to fold and cut a Christmas star

By Christian Lawson-Perfect. Posted December 24, 2022

This week and last I hosted a series of public maths talks featuring disabled presenters. I’ll post about how that went later, but for now I just want to share this clip of me filling time spreading Christmas joy.

This is a party trick that Katie Steckles showed me: you can fold a piece of paper and then make a single cut to produce a five-pointed star. I showed how to do it by following the instructions I’d been told, and then recreated the steps just starting from the insight that when you make the cut, all the edges of the shape need to be on top of each other.

Maybe you’ll show someone else how to do it during the Christmas holiday?

This doesn’t only work for stars: there’s a theorem that you can make any polygon by folding and a single cut. Erik Demaine has made a really good page about the theorem, with some examples to print out and links to research papers. Katie can cut out any letter of the alphabet on demand, which is impressive to witness!

What Can Mathematicians Do? A series of online talks about maths

By Christian Lawson-Perfect. Posted November 9, 2022



I’ve put together a series of online public maths presentations, to take place in the last couple of weeks of term before Christmas.

This came about after a few people on the Talking Maths in Public WhatsApp group complained that we can hardly ever take up requests for a speaker to deliver a fun maths talk due to our disabilities, usually because of the difficulty of travelling to and from an event. I quipped that we should set up a series of talks for non-commutative mathematicians, and then I was told that the department’s EDI committee had a load of money sitting unused in its budget. So I decided to use some of it!

Integer sequence review: A101544

By Christian Lawson-Perfect. Posted August 13, 2022

It’s nine years since the first integer sequence review, and six years since the last one. We’ve grown as people, and in CLP’s case, grown people. The world has changed, but our love for the Online Encyclopedia of Integer Sequences hasn’t.

A101544

Smallest permutation of the natural numbers with $a(3k-2) + a(3k-1) = a(3k)$, $k > 0$.

1, 2, 3, 4, 5, 9, 6, 7, 13, 8, 10, 18, 11, 12, 23, 14, 15, 29, 16, 17, 33, 19, 20, 39, 21, 22, 43, 24, 25, 49, 26, 27, 53, 28, 30, 58, 31, 32, 63, 34, 35, 69, 36, 37, 73, 38, 40, 78, 41, 42, 83, 44, 45, 89, 46, 47, 93, 48, 50, 98, 51, 52, 103, 54, 55, 109, 56, 57, 113, 59, 60

Presenters wanted: a series of public maths talks by disabled mathematicians

By Christian Lawson-Perfect. Posted August 2, 2022

I’m organising a series of online public maths talks through my work, the School of Maths, Stats and Physics at Newcastle University.

The point is that talks will be delivered by disabled presenters. This came about because I and some other disabled people who do maths talks got tired of missing out on opportunities to do outreach because it involves travelling. Not every disability makes travelling harder, but we felt that there were enough people excluded by in-person events that it would be nice to put on a more accessible event.

My aim is for this to take place in December 2022, near to the International Day of People with Disabilities. Talks can be any mathy topic, or about your experience as a disabled mathematician.

I need speakers!

To give some idea of what I’m looking for, I’ll use myself as an example. I count myself disabled at least four ways: I’m colourblind, autistic, dyspraxic, and have Ehlers-Danlos syndrome.

I might talk about:

• Use of colour in mathematical communication, for example how red chalk makes chalk-and-talks inaccessible.
• How ambiguously-worded maths problems have stymied me in the past, and how to write them more clearly.
• Integer sequences, which is just something I’m interested in.

The sessions will be delivered over Zoom, with live captions written by humans and a BSL interpreter. (If you can recommend a BSL interpreter with experience of interpreting maths talks, please get in touch!)

We’ll be advertising the talks to the general public, both grown-ups and schools, so I’m not looking for talks about high-level maths or education research.

This is open to anyone around the world, but if you’re a long way from the UK bear in mind that we’ll schedule the sessions at a convenient time for a British audience.

If you’re interested in taking part, please email christian.perfect@ncl.ac.uk.

I’d like to have a list of presenters by the end of September, to leave plenty of time to arrange whatever needs to be arranged and to advertise the talks.

Prime Run

By Christian Lawson-Perfect. Posted May 30, 2022

Here’s a game I’ve been trying to make for a while.

For a while I’ve had a hunch that there’s fun to be had in moving between numbers by using something related to the prime numbers.

Over the years I’ve tried out a few different ideas, but none of them ever worked out – they were either too easy, too hard, or just not interesting. This time, I think I’ve found something close enough to the sweet spot that I’m happy to publish it.

Prime Run is a game about adding and subtracting prime numbers. You start at a random number, with a random target. Your goal is to reach the target, by adding or removing any prime factor of your current number.

Didn’t Graduate Texts in Mathematics

By Christian Lawson-Perfect. Posted May 27, 2022

Every now and then a phrase pops into my head and won’t leave until I write it down or tell it to someone else.

One day the little voice in my head suggested putting “Didn’t” before the classic series of maths textbooks, Graduate Texts in Mathematics.

So I found a cover of a GTIM book, stuck “Didn’t” on the front and changed the title to an in-joke about not understanding category theory, and was happy with my life.



But then I thought that it would make sense to make a whole series of these, so I spent a couple of hours making a meme generator.

And then I tooted and tweeted it.

The Aperiodical is 10!

By Peter Rowlett, Katie Steckles and Christian Lawson-Perfect. Posted April 25, 2022



Not that we’re overly consumed with numerical coincidences, but it’s perhaps nice to note that ten years ago today we made a little fuss of launching a new blog site with our first post, a post marking Felix Klein’s 163rd birthday, and a video about the Klein Bottle featuring Matt Parker and Katie Steckles.