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You might not have realised, but today is ‘Twosday’ – an extremely exciting day for mathematicians

The date is 22.2.22, a beautifully satisfying symmetric palindrome, reading the same forwards as it does backwards

Kit Yates
Tuesday 22 February 2022 09:57 GMT
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<p>Mathematicians are getting excited about today’s date: 22 February 2022</p>

Mathematicians are getting excited about today’s date: 22 February 2022

Today is an exciting day. It’s “Twosday Tuesday”. Don’t worry if you’ve never heard of it though, it’s just a bit of fun. Mathematicians are getting excited about today’s date: 22 February 2022.

OK, so it doesn’t look so special when written out like that. Convert it into numeric form, however, and it transforms into 22.2.22, a beautifully satisfying symmetric palindrome, reading the same forwards as it does backwards. The fact that it happens to fall on a Tuesday is just the icing on the cake. Unusually, this palindrome also has cross-border acceptance: even if you use the American month/day/year format it’s still 2.22.22.

Typically, the longer a palindrome is, the rarer it is – and the rarer something is, the more we tend to appreciate it. You’ll have come across many short palindromic words like “mum” and “dad”, even if you didn’t know what a palindrome was before now. They’re cute but relatively easy to find.

For me, the more satisfying wordy palindromes are the longer ones which still read like a coherent sentence. For example, one can imagine the Bible’s first man breaking out the line “Madam in Eden, I’m Adam”, upon first meeting his palindromic partner, Eve. Another famous favourite, often incorrectly attributed to Napoleon Bonaparte, goes: “Able was I ere I saw Elba”. It alludes to the emperor’s forced abdication and subsequent exile on the Mediterranean island of Elba. Of course, there are longer entries, including a 540-worder, found by extending the well-known “A man, a plan, a canal, Panama!” palindrome, but these really long ones don’t tend to make too much sense.

When it comes to numbers, there’s no limit to length, but the palindromes do get rarer the bigger they are. There are nine palindromes below 10, but only 19 below 100. There are 109 in the first 1,000 positive numbers, but only 90 more in the next 9,000. So for me, purely because of its rarity, I’ll be writing today’s date in its alternative long UK format: 22.02.2022 – an eight-digit palindrome.

But why, you may ask, is any of this important? The answer is that it really isn’t, which is part of what makes it enjoyable. Although there are some theoretical applications of palindromes in the compression of DNA sequences, they fall very much into the arena of “recreational maths”. I guess that many people reading this will imagine that they might never have encountered a more oxymoronic concept, but the number of people doing maths for fun in the United Kingdom is growing.

Sudoku’s enduring popularity is evidence of the appeal that even naked mathematics (in the form of logic) can have as a pastime. But there are broader areas in which mathematics underlies entertainment. Many magic tricks rely on mathematical sleights of hand, whilst juggling and origami are inherently mathematical pursuits. Many of the games we play, from Twenty-One to Monopoly, require us to actively do simple mathematics to participate. Players of dominos, noughts and crosses and rock-paper-scissors benefit from mathematical strategizing without necessarily needing to do maths to play the game.

Some pastimes like the Rubik’s cube or Dobble have extremely deep mathematics underlying their structure. Even Wordle, the five-letter guessing game that has taken the world by storm, draws on the mathematical ideas of information entropy and frequency analysis to optimise solution-finding. These are amongst the very same techniques employed by the mathematicians of Bletchley Park, whose code cracking efforts are often credited with shortening the Second World War.

Beyond the renaissance experienced by parlour games during the pandemic, the growing popularity of recreational maths is embodied by MathsCity, the UK’s first interactive mathematics discovery centre, based in Leeds. Run by MathsWorldUK, the charity for which I act as a trustee, the exploratorium is crammed full of hands-on puzzles and arresting exhibits which demonstrate the power, utility and ultimately, the enjoyment of maths.

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In a more colloquial setting, for over a decade the MathsJam organisation has supported regular, weekly gatherings of like-minded individuals up and down the country. Friends get together in the pub to share ideas, play games or even swap mathematical knitting tips. Often the whole evening can pass solving problems like the one we began with - finding palindromic dates.

So you shouldn’t worry if you’re coming to this article late, and you’ve missed Twosday Tuesday. There are plenty more palindromes to be found in February 2022 alone (if you’re prepared to use the five-digit American month/day/year). Most of the months of 2022 contain a palindrome using the five-digit British day/month/year format. If you’re really prepared to bend the rules, then you can even enjoy a palindrome in the backwards five-digit year/month/day format before the year is out.

Why not set yourself a challenge and find the next palindromic date? I’ll leave the answers as a piece of recreational maths for you to figure out. When you correctly solve the problem, the dopamine hit that keeps so many of us hooked on the subject will make it worth your while. And the great thing is you’ll never run out of dates to find. Maths is the gift that keeps on giving.

Kit Yates is director of the Centre for Mathematical Biology at the University of Bath and author of The Maths of Life and Death

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