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## Happy pi day, Albert!

What a lovely coincidence! Pi day (the 14th of March, written 3.14 in the US) is also Albert Einstein's birthday. How are you going to celebrate? You could join Marcus du Sautoy and over a thousand other people in a mass online experiment to calculate pi or you could join *Plus* in Cambridge to watch our favourite mathematical movie Travelling Salesman. And to celebrate both the number and the man, here are some favourite articles.

How to add up quickly

One of our favourite authors, Chris Budd, takes a look at some famous infinite series involving pi and presents a trick for making them converge quicker.

Einstein as icon

In 1905 Albert Einstein changed physics forever with his special theory of relativity. Since then his name — and hair do — have become synonymous with genius. John D. Barrow looks at Einstein as a media star.

What is the area of a circle?

You might know the famous formula for an area of a circle, but why does this formula work? Tom Körner's explanation comes with a hefty estimate of pi.

What's so special about special relativity?

Most of us are aware that Einstein proved that everything was relative ... or something like that. But we go no further, believing that we aren't clever enough to understand what he did. Hardeep Aiden sets out to persuade you that they too can understand an idea as elegantly simple as it was original.

Pi not a piece of cake

Every phone number on the planet, all of our names (with the characters suitably encoded), even the works of Shakespeare can be found in the digits of pi — if these digits are truly random that is. So are they?

How does gravity work?

Einstein's theory of general relativity doesn't look at gravity as a force, rather it replaces the concept of force by that of geometry. How does that work?