A number of things to know about Pi

Story highlights

  • Pi Day is celebrated March 14 in honor of the famed irrational number
  • San Francisco's Exploratorium and Princeton, New Jersey, go all out

(CNN)Math enthusiasts know all about it, and the rest of the population is probably hoping for cherry pie.

But March 14 is Pi Day. While last year stretched the symbolic celebration out a little longer -- to 3.1415 -- each year presents ample opportunity for learning.
To 31 decimal places, the celebrated irrational number that never ends is 3.1415926535897932384626433832795.
A few more tidbits about pi and Pi Day:
About pi
Pi is the ratio of the circumference of a circle to its diameter. It's not equal to the ratio of any two whole numbers, so an approximation -- 22/7 -- is used in many calculations.
Pi is essential in architecture and construction and was used frequently by early astronomers. Pi has been known for about 4,000 years, but it started to be called by the Greek letter only in the 1700s.
Pi Day deals
Sweet and savory pie lovers are in luck after all. Pizza Hut is offering the chance to win free pizza for 3.14 years to those who can solve math problems posted on its web site.
Microsoft is discounting select Dell PCs by 31.4%.
Participating Whole Foods stores are offering $3.14 off the regular price of pies, plus $2 off pizzas on March 14.
The origin of Pi Day
Pi Day started 28 years ago at San Francisco's Exploratorium.
Physicist Larry Shaw, who worked in the electronics group at the museum, started celebrating pi on March 14, 1988, primarily with museum staffers. The tradition has grown to embrace math enthusiasts from all walks of life.
This year, the Exploratorium is hosting a day-long celebration at its facility on Pier 15, including a Pi Procession, pi "explorables" and servings of pie.
Pi Day is also Albert Einstein's birthday. In Princeton, New Jersey, where Einstein lived for more than two decades, signs of the scientist permeate the Pi Day festivities, which span five days culminating on March 14 with Nerd Herd smart phone pub and grub crawls.
For more about pi, visit www.piday.org.