### Happy Birthday Euler!

Today is Euler’s $-306 \times e^{i \pi}$th birthday, and Google have chosen to celebrate (despite ignoring several other prominent mathematical birthdays, including Erdős’s centenary – see the @MathsHistory twitter feed for a full list) by creating a Google doodle on their homepage.

For anyone who isn’t aware, this is when Google changes the image above the search box on the homepage at Google.com, so it still says ‘Google’ but using an appropriate image, which sometimes has built-in interactive elements. I thought it was worth pointing out some of the fantastic maths they’ve included in today’s doodle.

It’s Friday again! And with a seamless unbroken chain of Follow Friday posts stretching backward through time with no discernible gap, here’s another post with some recommendations of people to follow on Twitter if you’re into maths.

### f(Erdős) = 100

Today is the 100th anniversary of the birth of Paul Erdős, or as most people would call it, Erdős’ 100th birthday. So, Happy Birthday Paul. And if you’ve never heard of him, let’s see what people at his birthday party are saying about the Man Who Loved Only Numbers. Please note: all birthday parties are strictly fictional.

Probably the greatest mathematician of the twentieth century, Paul Erdős … was so eccentric that he made Einstein look normal. He was 11 before he ever tied his shoes, 21 before he ever buttered toast, and died without ever boiling an egg. Erdős lived on the road, traveling from conference to conference, owning nothing but math notebooks and a suitcase or two. His life consisted of math, nothing else.

– Clifford Goldstein, in The Mules That Angels Ride (2005), p. 125

### Open Season – The Perfect Cuboid

In this short series of articles, I’m writing about mathematical questions we don’t know the answer to – which haven’t yet been proven or disproven. This is the second article in the series, and considers a less well-known variant on an extremely well-known problem.

Ask anyone to name a theorem, and they’ll probably come up with one of the really famous ones, like Pythagoras’ theorem. This super-handy hypotenuse fact states that for a triangle with sides A, B and C, where the angle between A and B is a right angle, we have $C^2 = A^2 + B^2$. This leads us on to a nice bit of stamp-collecting – there are infinitely many triples of integers, A, B and C, which fit this equation, called Pythagorean Triples.

One well-known generalisation of this is to change the value $2$ to larger values, and go looking for triples satisfying $C^n = A^n + B^n$. But don’t – Andrew Wiles spent a good chunk of his life on proving that you can’t, for any value of $n>2$, find any such triples. The statement was originally made by Pierre De Fermat, and while Fermat famously didn’t write down a proof, it was the last of his mathematical statements to be gifted one – hence the name ‘Fermat’s Last Theorem’ – and proving it took over 350 years.

### Foldable Dodecahedron Calendar made in LaTeX

If anyone still hasn’t sorted themselves out with a calendar for 2013 – come on people, it’s February! – there’s a nice example of one here. It’s a dodecahedron which, once assembled, you can presumably orient to display the correct month (or the incorrect month, if you’re an impish sort).

The best thing about it for fans of LaTeX (the majestic mathematical markup language of kings) is that this thing is written entirely in LaTeX, using the TikZ package to create the graphics.

Download: PDF and TeX files, as well as all necessary packages, are available from TeXample.net.

(If you can’t compile the calendar yourself and want an up-to-date version, click on the Open in writeLaTeX link).

### ‘Of little practical value’?

Some mathematics, pictured here being hard to illustrate in news coverage

As the heady excitement of the dawn of a forty-eight-Mersenne-prime world dims to a subdued, albeit slightly less factorable, normality, I have taken the opportunity to see what we can learn about the British press’s attitude and ability when it comes to the reporting of big numbers ending in a 1.

Overseas readers may not be aware that the UK’s public service broadcaster, the BBC, is funded by a mandatory annual £145.50 tax on all television-owning households. Therefore, it would be disappointing if some of these funds were not channeled into reporting the discovery in at least five or six separately-produced broadcasts across the organisation’s various radio and television outlets.

### Open Season – Singmaster’s Conjecture

Science and maths are all about finding things out. Mathematics in particular is about making statements, and then determining their truth (or falsity). Finding a proof, or disproof, of a mathematical theory can be as simple as finding a counterexample, or it can take hundreds of authors tens of thousands of pages.

In this short series of articles, I’m going to write about some mathematical questions we don’t know the answer to – which haven’t yet been proven or disproven. Hopefully you will find it interesting, and maybe someone will even be inspired to delve deeper and find the answers themselves.