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Santa’s sack of scientific surprises

This post was part of the Chalkdust 2016 Advent Calendar.

Welcome to the third day of the 2016 Chalkdust Advent Calendar.  Today, we bring you some fascinatingT&Cs apply facts, randomly generated by Santa’s elves.  Please send us your favourite scientific curiosities either on Facebook, Twitter or email and we’ll feature the best in a blog next year.

### The number 3

The Tre Cime di Lavaredo, iconic symbols of the Italian Dolomites

Today is the third day in your advent calendar. Three is the largest number that, when written in Roman numerals (III), requires the same number of strokes as the number itself. Less interestingly, it is the first odd prime number. More interestingly, it is the only number that is both a Fermat prime (can be written as $2^{2^n} + 1$) and a Mersenne prime ($2^n-1$). It is also the only prime that is one less than a perfect square. Prove it.

### Feeling blue

The ancient Greeks had no word for the colour blue. Despite, presumably, the sky being as blue back then as it is now (due, by the way, to Rayleigh scattering: blue wavelengths of light are scattered more widely by the oxygen and nitrogen molecules in the air, meaning that more blue reaches our eyes). The pigment blue was, however, incredibly hard to make (although those clever folk in Egypt cracked it) and, in a dramatic modern non-twist, creating blue LEDs proved to be beyond the skills of humanity until the 1990s. The scientists who succeeded won the Nobel prize in 2014 and, more impressively, were featured on our very first On the cover. We have unfortunately been unable to ascertain whether the first ancient Egyptians to make blue dye ever had the equivalent honour.

### Pub crawler

Next stop: that way!

In one of the most impressive and useful pieces of research carried out over the last couple of years, a team of mathematicians led by Professor William Cook at the University of Waterloo (Canada), mapped the shortest possible route between 24,727 pubs in the UK. Its length: over 45,000km. Longer than the circumference of the Earth. This is an example of the travelling salesman problem. Or the very drunk travelling salesman problem.

### The average you

The average human has one testicle and one ovary. The standard deviation, however, is huge.  And on that note, I leave you.  Until next time!

[Pictures. Tre Cime di Lavaredo: Federico Galber, used with permission; Chalkdust Issue 1 cover: Chalkdust and Anthony Lee; Pub: The Dublin Castle, picture by the author, used with permission from himself]

Pietro is interested in history and sport. He also happens to be doing a PhD in fluid dynamics at UCL. If he can combine any two of the three it makes him a happy man.
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