This story was first published on March 14, 2015, and updated on March 14, 2018.
On Wednesday (March 14), mathematicians and nerds around the world will honour the most widely known mathematical constant and irrational number - Pi or approximately 3.14.
Since the day was first marked at San Francisco's science museum, the Exploratorium in 1988, it has gained in popularity.
Science Centre Singapore is organising games and activities to celebrate the day, which is also Albert Einstein's birthday. These include a memory game challenge for the most number of post-digits of Pi, and the opportunity to make a "climbing" Einstein toy.
Nasa is also having its own "Pi in the Sky" challenge, which involves using Pi to solve math problems faced by its scientists and engineers, such as calculating for Martian earthquakes, helium rain on Jupiter and the rotation rate of the first interstellar visitor ever discovered - asteroid 'Oumuamua.
Here are 14 funky facts about pi and Pi Day:
1. Defined as ratio of the circumference of a circle to its diameter, pi is all around us. The number is the same for all circles of any size.
2. Pi is an irrational number, which means it is an infinite decimal and the number never ends. While you may remember using 3.14 or 22/7 in your geometry homework, computer programmes have calculated its value up to trillions of decimal places.
3. Only 40 digits of pi is needed to accurately calculate the spherical volume of the universe, but mathematicians find it a challenge to figure out and memorise the digits of Pi.
4. The Guinness world record for memorising the digits of pi is held by Chao Lu of China, who recited the number to more than 67,000 decimal places.
5. Pi has been known for almost 4,000 years, but ancient civilisations such as the Babylonians did not have accurate calculations of it. The first calculation of pi was done by Archimedes (287-212 BC).
6. The Exploratorium's physicist Larry Shaw started the tradition of celebrating Pi Day, and they marked it in 1988 by walking around in a circle while eating fruit pies.
7. The US Congress endorsed Pi Day as a day to celebrate math education in 2009. Many institutions mark it as a way to encourage interest in math and science.
8. There are now many events held in conjunction with Pi Day in the US and worldwide. Some involve eating pies, others the memorising of the digits of pi, and other educational activities that 'pi-ticipants' can enjoy.
9. In the Greek alphabet, the Pi symbol (π) is the 16th letter. It is pronounced "piwas" in Greek. Coincidentally, the letter "p" is also the 16th letter in the English alphabet.
10. There is a song about pi by British singer Kate Bush.
11. Some people bake Pi pies.
— City A.M. (@CityAM) March 11, 2015
12. Brace yourself for pi(e) puns and jokes.
— Trinity Rouser (@11thHourLib) March 3, 2015
13. July 22, or 22/7 is Pi Approximation Day.
14. March 14 is also scientist Albert Einstein's birthday. Just a coincidence?