International Pi Day, which falls on March 14 (also the birthday of renowned scientist Albert Einstein) every year, honours the most widely known mathematical constant and irrational number - approximately 3.14.
It is best defined as the ratio of the circumference of a circle to its diameter.
Pi Day has been celebrated by mathematicians and number lovers around the world since it was first marked at the San Francisco Exploratium in 1988.
Prime Minister Lee Hsien Loong, a former senior wrangler at Cambridge University, has written a Facebook post for the third year running explaining Pi Day's significance.
Here's a look at how this year's Pi Day is being celebrated.
Singapore Science Centre's Festival of Numbers
The centre's ongoing Festival of Numbers, which runs till Sunday (March 19), features a Pi Day element.
A hundred visitors will be tasked to form the circle of Pi at the atrium at 1.59pm on Tuesday.
Other activities at the festival include a tinkering studio for geometric shapes, math talks and workshops, as well as a Rubik's cube demonstration.
Nasa's Pi in the Sky 4 challenge
The US space agency has challenged students to use pi to solve real-world science and engineering problems as part of its illustrated problem set series.
They include calculating the angle of crater impacts on Mars and measuring the size of the shadow that will fall on North America during this year's total solar eclipse.
Explaining the importance of pi, Nasa said: "While many of us celebrate by eating pi-themed pie and trying to memorise as many digits of pi as possible (the record is 70,030 digits), scientists and engineers at Nasa take pi even further, using it in their day-to-day work exploring space!"
Free entry to San Francisco Exploratium
At ground zero of where it all began, entry is free for all visitors to mark the 30th anniversary of Pi Day.
It has promised to serve up pi-themed activities, rituals and yes, plenty of pie.
Those who can't join the celebrations in person can do so via the 3D virtual world Second Life, where pi exhibits have been created for users' avatars to explore.
MIT's superhero-inspired video
At the Massachusetts Institute of Technology (MIT), coming up with a Pi Day video has become an annual tradition to tout its habit of sending out acceptance letters on March 14.
Its video this year stars Marvel character Riri Williams, who is accepted into MIT at the age of 15 and proceeds to construct an Iron Man-like suit of armour.
Last year's video feature Star Wars droid BB-8, while drone were main attraction in 2015.
Stuff your face with pie (or pizza) in Chicago
Pie shops love Pi Day - it's a chance for them to roll out their pi-related $3.14 promotions and cash in.
This year, 21 bakeries and restaurants in Chicago are getting in on the action, reported the Chicago Tribune.
The selection consists of mainly sweet pies, with a couple of pizzas thrown in.
