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Prize crossnumber, Issue 21

Our original prize crossnumber is featured on pages 66 and 67 of Issue 21.

Rules

  • An over-zealous copy editor has ‘corrected’ this crossnumber. In the original puzzle, every clue was of the form abA or abD, where a and b are positive integers, and † is +, –, ÷, or × (and A and D stand for across or down); the copy editor then took every clue, calculated ab, and replaced ab with the result. For example, if a clue now reads ‘6A’, then the actual clue could be:
    • 0 + 6A,
    • 3 + 3A,
    • 12 – 6A,
    • 1 × 6A,
    • 2 × 3A,
    • 6 ÷ 1A,
    • 120 ÷ 20A,
    • or many other things…
  • There is only one solution to the completed crossnumber. Solvers may wish to use the OEIS, Python, a team of 300 volunteers with abacuses, etc to (for example) obtain a list of prime numbers, but no programming should be necessary to solve the puzzle. As usual, no entries begin with 0.
  • One randomly selected correct answer will win a £100 Maths Gear goody bag, including non-transitive dice, a Festival of the Spoken Nerd DVD, and much, much more. Three randomly selected runners up will win a Chalkdust T-shirt. Maths Gear is a website that sells nerdy things worldwide, with free UK shipping.
  • To enter, submit the sum of all the digits in the row marked by arrows using this form by 25 September 2025. Only one entry per person will be accepted. Winners will be notified by email and announced on our blog by 1 November 2025.

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Dear Dirichlet, Issue 21

Moonlighting agony uncle Professor Dirichlet answers your personal problems. Want the prof’s help? Send your problems to deardirichlet@chalkdustmagazine.com.

Dear Dirichlet,

Wedding season is coming up and I realise I need to get my suit slightly ‘adjusted’, shall we say. My local high street has a few places which offer services, but I’m hoping to get it done as economically as possible. What should I ask for?

— Mervin Miles, London NW3

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Book of the Year 2024

A few weeks ago, we announced the shortlist for the 2024 Chalkdust Book of the Year. We award two prizes: the Chalkdust Book of the Year (as chosen by our editors), and the Chalkdust Readers’ Choice (as voted for by our readers).

Chalkdust Book of the Year 2024

The winner of the Book of the Year 2024 was picked from the shortlist by the Chalkdust editors:

Think Twice

Alex Bellow

This book (Penguin, Waterstones) is Alex’s latest book all about the puzzles that most of us get wrong.

You can also read our full review of Think Twice here.

Chalkdust Readers’ Choice 2024

As well as picking our favourite from the shortlist, we held a vote for our readers to pick their favourite. The runaway winner of this poll was:

Mapmatics

Paulina Rowin´ska

This book (Blackwell’s, Waterstones) is all about the mathematics of maps and how the maps we use shape how we view the world around us.

You can read our full review of Mapmatics here.

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Cryptic crossword, Issue 21

Cryptic #9, set by Kelpie: Download as a PDF or solve below!

Across clues

  • 1. Ordinary counting number. (7)
  • 4. Basic statements about first accepted unknown charged atoms gaining mass by losing neutron. (6)
  • 7. Divine blood from one refrain swallowing oxygen. (8)
  • 8. A flat topped cone? Made from iron last. (3)
  • 9. Illinois elevated railways made from initially electric locomotive siding. (3)
  • 11. I’m after initially tough review clip. (4)
  • 14. A candle on fire. (6)
  • 15. Mark spring cleaning instrument without initial extension rod head for magazine. (9)
  • 16. Valley seen in shaping lens. (4)
  • 17. Endless untruths, Sophus? (3)
  • 19. Centres of attention? An ellipse has two. (4)
  • 20. Ode moving brood. (4)
  • 21. Units of area measurement augmented reality. (2)
  • 22. Endless frost forms an edge. (3)
  • 24. Outpouring from heads of joint European team. (3)
  • 25. Papers I initially devoured. (2)
  • 26. Quite easily demonstrated leads the way for ending proofs. (3)
  • 28. Continuous or discrete? Transformation leaves an object unchanged! (9)
  • 30. Eco-friendly son of a baker. (5)

Down clues

  • 1. Type of analysis studies refashioned minute unclear line. (9)
  • 2. Spin tornado without hesitation. (5)
  • 3. Egyptian sun god starts to really admire Helios. (3)
  • 5. On the back page, put tea in them after contest. (4,3,4)
  • 6. Kingly community is oldest scientific academy. (5,7)
  • 10. A sailor’s drink without Romeo? Shocking! (4)
  • 12. Sacrilege hiding upset. (4)
  • 13. This topologist’s an Irish son of a … cartoon beer? (6)
  • 18. I say, it is in the same source. (4)
  • 20. First-rate notation for a derivative. (5)
  • 22. Field perhaps? found in superstring. (4)
  • 23. Vhat, Vhere, …? Sounds like our favourite diagram creator. (4)
  • 27. Sounds like I contained in Disneyesque facial feature. (3)
  • 29. My uncle initially sounds like a cow. (2)

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The big argument: Calculators – phone or physical?

Physical, argues Elinor Flavell

Ah…, the humble calculator.

The mathematical chic accessory. Whip a calculator out at random intervals, and it will do to you what taking off glasses did to girls in 90s rom-coms.

No phone calculator can compare! Ask yourself: How often do you reach for your calculator? `All the time’ I hear you say. Because:

  • it always has charge,
  • you don’t need to upgrade it every 18 months, and
  • it is very hard to scratch (as my calculator can bear testament to).

Calculators are the one friend that cockroaches will have in the apocalypse.

In comparison, how often do you reach for the calculator on your phone, try to work something out, and then sigh because it is just not easy to get the answers you are looking for? How often do you have to Google how to write $\sin^{-1}x$ on your phone calculator? `All the time’ you say! That sounds rather like a phone calculator isn’t up to the job…

For me it’s a no brainer. The best calculator is the one that never runs out of battery, always works, and makes you look like a nerd. Why use anything else? Stay strong to the calculator.

Phone, argues Sophie Maclean

Firstly, before I put forward my case, I must dispute the phrasing of this argument. Phone calculators vs ‘physical calculators’? Phone calculators are physical calculators. To say otherwise is pure intellectual snobbery. Especially now that phone calculators are often equipped with the functions of scientific calculators.

But semantics aside, a phone calculator is orders of magnitude (which you can work out easily on this little app) better than a handheld calculator. It can do everything a handheld can do, and more. Why would one opt for a device with less functionality, over the one that they carry around anyway?! If I were to start using a handheld calculator, I would still be carrying my phone (and therefore phone calculator) with me anyway.

I am not exaggerating to say that I have not used my handheld calculator since my final A-level exam. Outside of the totalitarian simulation of real life that is the English school system, I am either capable of doing the necessary calculations in my head, already have my phone on me, or am in need of a tool much more powerful than a handheld calculator can give.

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What’s hot and what’s not, Issue 21

Maths is a fickle world. Stay à la mode with our guide to the latest trends.

HOT Releasing things in two parts

Dune and Wicked both show us that the real trick for writing is to set up your problem really well, then leave the reader hanging for a year.

Ariana Grande and Cynthia Erivo

Image: Our Movie Guide, CC BY 3.0

NOT Cramming your research into one long paper

The first half is necessary and sufficient to get it nominated for a bunch of awards. And no one’s going to sit through a six-hour proof without needing the loo, anyway.

HOT 90s reunions

Oasis and 5ive leading the charge. Expect Andrew Wiles to re-prove Fermat’s last theorem on his UK arenas tour this summer.

Oasis

Image: Will Fresch, CC BY-SA 2.0

NOT Anything 2025

Can we just hide from the news?

HOT MathTok

Function dances, pretty notetaking and Howie Hua. If it encourages anyone to improve their handwriting, mathematics will be in a better place.

NOT BookTok

Like MagazineTok but longer, in black & white, and without fun features like this.

HOT Glambots

Fast-shutter slo-mo videos for the red carpet, but also available to capture the exact moment you realise you missed a minus sign two pages back.

NOT Spambots

Dear Surname, First Name Initial. You are invited to a…

HOT Potatoes

Better for frying, but OK at flying.

NOT Prime Target

Everyone secretly hoping they’re on the Americans’ list of ‘European mathematicians who might find a deadly prime number’. There are better things to watch on Apple TV+.

HOT Slow Horses

Series 5 is based on the best book.