Last weekend, number nerds and pastry lovers around the world celebrated what was quite literally a once-in-a-century event.

Pi Day (March 14) appears on the calendar every year and was officially recognized by the United States House of Representatives in 2009. But it was this year that the world could celebrate Ultimate Pi Day.

In the fifteenth year of every century, the calendar makes it such that the first five digits of pi—3.1415—appear in order in the numerical representation of the date. Add to the date the element of time, and you can extend as far as the tenth digit at 9:26 and 53 seconds, a.m. or p.m.

Much like the figure that the Greek letter represents, the number of ways you can celebrate Pi Day is endless, and associations across many industries join to mark the occasion each year. Here’s a look at how some groups latched onto the excitement of Ultimate Pi Day on Saturday.

Mathematical Association of America. Ultimate Pi Day happened to fall in the year when MAA is celebrating its 100th anniversary. MAA, which calls itself the largest professional society whose mission is to “advance the mathematical sciences, especially at the collegiate level,” asked the public to submit pi-related photos for its Pi Day Facebook gallery and provided links to activities that teachers could use to celebrate Pi Day in the classroom.

Pi Across America. The group dedicated entirely to spreading the good news about pi—for free—also is home to one of the largest databases of Pi Day events and activities. “We are pleased to note that over tens of thousands of teachers and others visited the Pi Across America website throughout the year, but especially around March,” cofounder David Quick said in a statement [PDF]. “Math can be fun and engaging, and hopefully the resources we are providing will help educators in their vital quest to make America’s students as competitive as possible in an increasingly competitive world economy.”

American Pie Council. A Pi Day celebration wouldn’t be complete with actual pies. APC served up a National Pi(e) Day packet [PDF] with activities, facts, and recipes related to pi and pies. (Did you know that apple pie, which can be made 231 different ways, is the favorite pie of 26 million Americans?) The group’s Pi Day website also contains pie-making tips, a section on the history of pie, and Food Network-style cooking videos.

How did you celebrate Ultimate Pi Day? Share your story in the comments.

(iStock/Thinkstock)