• Today (3-14) is PiDay! • Alright, today isn't really 3-14, it's 14-3. Alas, Pi Day is a purely American invention. But there are only 12 months in a year, and the UK will never have a 3-14, so we're going to have to pretend to be American just this once. • Pi (or π) is the ratio of any circle's circumference to its diameter. • The first mathematician to use the symbol π for this circular ratio was Welsh mathematician WilliamJones in 1706. He abbreviated the Greek word for perimeter ("περίμετρος"). • π = 3.1415926535 8979323846 2643383279 5028841971 6939937510 5820974944 923078164 0628620899 8628034825 3421170679... (etc etc etc, forever) • The digits of π never repeat (but there are six consecutive 9s at the 762nd decimal place, which is a bit unlikely). • π can't be represented by a fraction, because it's an irrational number. But 22/7 is quite close (0.00126 out), and 355/113 is astonishingly close (0.00000027 out). • If a circle has a diameter of 2 units, then its area will equal π units. • apple, banoffee, blackberry and apple, cherry, custard, key lime, lemon meringue, mince, mississipi mud, pecan, pumpkin • At the San Francisco Exploratorium, where Pi Day was initiated, they also celebrate Pi Minute at 3-14 1:59pm. This afternoon they'll be inviting visitors to sing the Pi Day song and then walk round the Pi Shrine 3.14 times (and then eat free pie). Here are some photos from Pi Day 2007 and 2008. • Pi Day is also Albert Einstein's birthday. • Piems are poems which represent π. You have to count the number of letters in each word to discover the sequence of digits. Here's a simple piem: "May I have a large container of coffee?" And here's a famous longer one: "How I need a drink, alcoholic of course, after the heavy lectures involving quantum mechanics." • In binary, π = 11.00100100001111110110… • The world record for memorising pi is currently held by Chao Lu who remembered 67890 decimal places in 2005. • Here are the first million digits of π (you may have to wait while it loads). The millionth digit is a 1. • The sequence of digits "...2009..." occurs within π at the 8184th decimal place. Meanwhile "...14032009..." occurs at the 46,555,644th decimal place. You can check any string of digits here. Or check your birthday here. • Take the Pi Day Challenge (Hmmm, I'm stuck on puzzle 1) • Kate Bush singsthe first 137 digits of π on her 2005 album Aerial. Unfortunately she omits the 79th to 100th decimal places (presumably in error). • chicken and mushroom, cottage, pork, shepherds, stargazy, steak and kidney, veal and ham • Listen to 15 minutes of π on Radio 4 • More π-related links here and here (and some geekier maths stuff here and here). • The second pizza theorem states that the volume of a pizza of thickness a and radius z = pi zz a
