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If you don't already know, pi day happens on March 14 (3-14) every year. Festivities include reciting digits of pi and eating pies. I understand that it's all in good fun, but I've always felt that pi day is bad PR for mathematics. To non-mathematicians, it gives the impression that mathematics is about voodoo numerology, memorizing (or computing) digits of pi, and bad puns. The bad puns part is pretty accurate, but I don't care for the others.

So I propose we come up with some alternatives to pi day that send a better message about what mathematicians do. If you've got an idea, post it here. If possible, include the following information about your proposed holiday:

  • when is it celebrated?
  • what are the festivities?
  • what kind of food would be associated with this day?

Please post only one proposed holiday per post. If you have more than one, please post multiple answers.

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    $\begingroup$ How about a math sex joke day? mathfail.com/2009/07/math-sex-jokes.html That ought to impress a commoner such as myself. $\endgroup$
    – user2814
    Commented Jun 26, 2010 at 2:35
  • $\begingroup$ Since my mother's birthday is June 28, I strongly advocate replacing pi day with 2 pi day. Speaking of this, my own birthday is April 9, so how about making this "squares of primes day." We could have some more of those: September 4, $\endgroup$
    – Michael Renardy
    Commented Jul 30, 2013 at 17:11
  • $\begingroup$ Last comment got cut off midway through for unknown reasons. You can fill in the rest. Anyway, I am voting to close. $\endgroup$
    – Michael Renardy
    Commented Jul 30, 2013 at 17:13
  • $\begingroup$ $\pi-1$ day is better. $\endgroup$
    – Joseph Van Name
    Commented Apr 7, 2019 at 11:58

12 Answers 12

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Pigeon-hole Day

Festivities include talking about proofs or arguments that use the pigeon-hole principle (I like that there are lots of these which are accessible). I'm sure there are also games you could come up with (e.g. n+1 people take turns throwing a coin at n jars. If you miss, you go to the back of the line. First one to put the second coin in a jar is eliminated and one jar is removed).

Food: not pigeons please. Maybe a cake with more than n interesting features being cut into n pieces.

One candidate for the day would be every blue moon (whenever there are two full moons in a month), but this only happens once every three years or so. Another idea is to try using the fact that every day of the week occurs 52 times in a year, except one, which occurs 53 times; I'm not sure of the best way to narrow it down from there.

Proposed choice of date:

Short answer: November 5th

Long Answer: I'm going to stick to nonleap years for a moment. So exactly one day of the week repeats 53 times. In 2009 this is a Thursday, so I'm going to say Thursday from there on out. If it is a different nonleap year, just replace Thursday by whatever day of the week happens on Jan 1st that year. You will get the same answer for the date.

Since every month has 4 or 5 of Thursdays, there exactly 7 months which have 4 Thursdays. So at least one quarter of the year has one or less 4-Thursday month. It turns out this is uniquely the 4th quarter, and the month is November. Further, it can't be November 1st or 2nd, because their days of the week happen 5 times. So there must be exactly one Thursday with a single digit date. This turns out to be November 5th.

November 5th is also the first time Thursday occurs on the same day of the month for the third time (February 5th and March 5th were also Thursdays.) And it's the farther Thursday in November from Thanksgiving.

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    $\begingroup$ Richard points out that musical chairs is the standard pigeon-hole game. $\endgroup$
    – Anton Geraschenko
    Commented Oct 19, 2009 at 19:51
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    $\begingroup$ Food being cut into n equal pieces using compass and ruler, that would be something. $\endgroup$
    – Ilya Nikokoshev
    Commented Oct 19, 2009 at 19:52
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    $\begingroup$ A knife is just a sharp ruler, Anton. $\endgroup$
    – Michael Lugo
    Commented Oct 19, 2009 at 21:05
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    $\begingroup$ Such a wonderful holiday should be celebrated more than once a year! I say we celebrate on the fifth Saturday of every month that has five Saturdays. $\endgroup$
    – Michael Lugo
    Commented Oct 19, 2009 at 21:06
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    $\begingroup$ Sounds like a good bar night. Some bars have events on the first and third Wednesdays of every month (for instance, that's when a professor I know plays bluegrass at the Albatross). Why not just say that pigeon-hole day is an event that happens on fifth fridays or something? I'm sure you can also come up with some interesting drinking games to play. You can also have a drink special - if a group of four people come to the bar together, then you get buy four get the fifth free. $\endgroup$
    – Kenny Easwaran
    Commented Oct 20, 2009 at 7:51
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Paradox Day, which happens on a random day during the year such that it is unexpected which day it is, except of course it couldn't happen December 31st because we'd know by December 30th that it'd have to happen the next day, so it couldn't happen December 30th by the same logic, and so on until January 1st, so logically the holiday couldn't happen, except it ends up happening anyway on say March 4th and is a total surprise.

Cake will both be provided and not provided.

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    $\begingroup$ A single slice of cake will be provided, and it's up to the organizers to cut it and distribute it so that everyone gets a whole slice. $\endgroup$
    – Steven Sivek
    Commented Oct 19, 2009 at 22:24
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    $\begingroup$ "Cake will both be provided and not provided." I think we've all learned not to trust anything anyone says about cake. $\endgroup$
    – Harrison Brown
    Commented Oct 19, 2009 at 22:35
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    $\begingroup$ This proposal seems to have picked up some support: spikedmath.com/271.html $\endgroup$
    – Doug Chatham
    Commented Jul 19, 2010 at 15:37
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I've always thought it was a bit silly to make such a fuss about a date that approximates some transcendental number rather than celebrate the birthday of a mathematician like Gauss, Ramchundra, or Hilbert (to name a very small subset of good choices). Individuals help to humanize the discipline, help the general public to understand why people choose to pursue mathematics, and most have very interesting life stories.

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Intermediate Value Day, celebrated every equinox (twice a year).

Food: avocados and persimmons, because they have to be just right to be delicious: too ripe, and they are rotten, too green and they are gross.

Games include that ball game that the French play, where the point is to throw your ball as close as possible to a special small ball.

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    $\begingroup$ That game is called Pétanque. $\endgroup$
    – Richard Dore
    Commented Oct 20, 2009 at 3:17
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Pi Approximation Day on July 22nd. (ie, 22/7)

I celebrate it every year, by going out in the summer and getting cake, instead of pie like we do in March. It's approximately pie :)

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How about Mathematics Awareness Month?

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  • $\begingroup$ At NMSU, we've apparently been celebrating that for some time. We get speakers from both inside and outside the math department. Seems like a good idea. Here's a blurb about this year's event: newscenter.nmsu.edu/?page=article&action=show&id=5087 $\endgroup$
    – Dan Ramras
    Commented Jul 19, 2010 at 18:26
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There's always $e$ day, which falls on the 72nd day of February (rounding 71.8 up). Note that which day in the usual calendar this is depends on whether it is a leap year.

In Europe, and actually everywhere that is not the US or Liberia, they celebrate $e$ day on the 27th day of Hexadecember (the 18th month), just like $\pi$ day in the rest of the world is on the 3rd of Dodecemeber.

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    $\begingroup$ I'm reminded of this Calvin and Hobbes comic: 3.bp.blogspot.com/_z1JyBxIESm8/SAE2DNGThkI/AAAAAAAACdo/… $\endgroup$
    – Kevin H. Lin
    Commented Jul 10, 2010 at 21:05
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    $\begingroup$ Eleventeen is one of my favourite numbers! :) $\endgroup$
    – José Figueroa-O'Farrill
    Commented Jul 11, 2010 at 0:00
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    $\begingroup$ In ancient times, I took a course from Richard Brauer, who once announced that the next homework assignment would be due on the 31st of February. Then, realizing what he had just said, he added, "which most people call the 3rd of March." $\endgroup$
    – Gerry Myerson
    Commented Jul 11, 2010 at 1:17
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We could celebrate Fibonacci Day on November 23 (US month/day ordering), with a particularly extravagant celebration planned for '58. The activities could include the burning of Dan Brown novels (creative use of propellants and accelerants encouraged), bisecting nautilus shells, and counting sunflower seeds.

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    $\begingroup$ I hardly think this is any less numerological than a fixation on the digits of pi. $\endgroup$
    – Qiaochu Yuan
    Commented Oct 20, 2009 at 3:09
  • $\begingroup$ My high school students enjoy learning about Fibonacci sequences since they are generated from "seeds," and are not just a string of numbers like pi (yeah, I know the deeper significance) the sequences occur in nature and are therefore "warmer," "more real" and less abstract than geometric shapes. They also like learning about checksums on credit/debit cards, but I can't think of a way to make a holiday about that. And they like learning at a general level about how music is transformed into bits on their iPods, but Fourier transforms and DFTs also seem unlikely holiday material. $\endgroup$
    – user790
    Commented Oct 21, 2009 at 9:03
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Guess what! Mole Day is this Friday. http://www.moleday.org/ Chemistry students everywhere will be celebrating.

I think Pi day is fine. It is not intended to convince the general public of anything. It is a fun activity for mathematics students.

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    $\begingroup$ The point is that it does send a message, and I think it's a bad one. Nobody will ever become interested in mathematics because of pi day. It's a crying shame that most people think mathematics is all about tedious calculations and memorization. Why not have a math holiday that accurately communicates why we love doing mathematics, where people might have "aha" moments that might lead to a life-long interest in the subject? $\endgroup$
    – Anton Geraschenko
    Commented Oct 20, 2009 at 14:59
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    $\begingroup$ re: Nobody will ever become interested in mathematics because of pi day. I don't believe this is necessarily true. Certainly I get a spike on visits my historical pi pages when pi day rolls around, and they involve discussions far off from the tedious calculations you cite. I also know people who discovered Buffon's Needle problem due to pi day; how is that not interesting mathematics? $\endgroup$
    – Jason Dyer
    Commented Oct 20, 2009 at 15:36
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Incompleteness Day. I don't know when it would be for sure (the last day of the first month on which the last day is not Saturday, perhaps?, but all party paraphernalia is either missing pieces or somehow inconsistent (e.g. clashing colors, discordant).

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    $\begingroup$ You could just do it on Gödel's birthday - I believe April 30 is the date. Pi Day is often observed in some localities as "Einstein's birthday", so this is a natural generalization. The only problem I see is that Gödel's theorems lend themselves to so much misinterpretation that it could end up turning people off of math rather than on. $\endgroup$
    – Kenny Easwaran
    Commented Oct 21, 2009 at 6:33
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    $\begingroup$ Incompleteness Day should be celebrated on the 29th of February in non-leap years. $\endgroup$
    – Gerry Myerson
    Commented Jun 2, 2010 at 3:24
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I recall one pi day at Penn State some grad students put up flyers announcing that they would construct a 65535-gon. Unfortunately I couldn't make it.

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For better or worse, Pi Day seems to be already fairly well established. I propose a modified Pi Day holiday 'weekend' which would aim to broaden its focus and break some of the stereotypes your question concerns, while cashing in on its 'name recognition'.

March 13. 313 is a twin prime and a palindrome, so there are plenty of ways we could go with this, although I can't think of any specific activities. It might be fun to kick off the festivities with an organized Trimathlon event - that is, some sort of grand scavenger-hunting, puzzle-solving, team competition.

March 14. Pi Day. I'd like to second the recommendation of Buffon's Needle related activities for this.

March 15 happens to be Leonhard Euler's birthday. As Mensen suggests, celebrating individual mathematicians helps humanize the discipline. Perhaps a famous-mathematican costume contest? Euler's contributions in particular are another source of activities; the video game Katamari Damacy is a great one to do with exponential growth.

EDIT: Removed a couple overly cynical remarks in the first paragraph expressing skepticism about whether alternatives would catch on with the general public.

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  • $\begingroup$ Huh? Wasn't Euler born on April 15, not March? $\endgroup$
    – Willie Wong
    Commented Mar 13, 2010 at 14:48
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    $\begingroup$ D'oh! I guess we'll have to spin off his birthday as a separate holiday, and March 15th can be "Ross has to learn the order of the months day"... $\endgroup$
    – Ross Churchley
    Commented Oct 15, 2010 at 23:48

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