Today is 22/7. No prizes for guessing what that means – yes, its Pi Approximation Day! March 14th (3.14) is also celebrated as Pi Day, but I kind of prefer the 22/7 version.

Pi, that curious little number that seems to pop up every time we start going in circles. A number so important that it even got its own name – not many numbers can claim that distinction!

Instead of going in circles trying to figure out what to give the kids for lunch, take your cue from the date and bake them a pi!

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Pi, or *π*, is a mathematical constant that represents the ratio between a circle’s circumference and its diameter, or *π* = C/d. It is what’s known as an irrational number – a number that cannot be expressed as a ratio between two integers. Being irrational, it has an infinite number of digits in its decimal representation, and it does not end with a repeating sequence of digits. It is also a trancendental number – a number that cannot be expressed with a finite sequence of algebraic operations.

In addition to its application in geometry and trigonometry, the constant *π* is found in many formulae, in a variety of sciences, including physics, number theory, thermodynamics, statistics, electromagnetism and mechanics.

The value of *π* (to 5 decimal places) is 3.14159, which is also approximately the value of 22 divided by 7. Calculating the value of *π* to higher and higher degrees of accuracy have been a challenge to mathematicians and computer scientists through the ages. Utilising the latest computing technology, the digital representation of *π* has now been calculated to more than 10 trillion digits. Memorising *π* to a large number of digits (a practice called *piphology*) is another challenge taken up by many pi-fanatics, and the current record stands at an astounding 67 890 digits, recited in 2005 in China by Lu Chao over a period of more than 24 hours. *(Wow, he probably doesn’t get out much!)*

A nice trick to remember the first few digits of pi is to use a poem or sentence where the lengths of the words correspond to the digits in pi. A well-known example, courtesy of English scientist James Jeans, is *“How I want a drink, alcoholic of course, after the heavy lectures involving quantum mechanics”*, cleverly representing pi’s first 15 digits.

Such is the pervasiveness of the number *π* that it can even boast numerous appearances in modern popular culture, from TV series (Simpsons, Twin Peaks) to novels (Carl Sagan’s “Contact”) to pop music (Kate Bush’s “Pi“).

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