For geeks, there are several great holidays on the calendar. There is of course Mole Day (10/23) to commemorate Avogadro’s number, which is huge (on the order of 1023) and hugely important in physics. There’s e Day (2/7) for Euler’s ubiquitous number (e = 2.718…). But the best is Pi Day, held on March 14 because the infinitely long decimal approximation of pi begins with 3.14. There’s so much to say about pi—I’ve been writing Pi Day posts for 14 years. (Here’s a partial list).
What is pi (or as the Greeks would say, π)? By definition, it’s the ratio of the circumference to the
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