#NationalYellowPigDay

What Is National Yellow Pig Day?

National Yellow Pig Day on July 17th is one of the most wonderfully absurd holidays you will ever come across. It started in the 1960s when two mathematicians at Princeton - Michael Spivak and David C. Kelly - developed an almost obsessive fascination with the number 17. Their deep dive into the properties of 17 led them to invent a mythical yellow pig with 17 eyelashes, 17 teeth, and 17 toes. What began as an inside joke between math enthusiasts eventually grew into a real celebration observed at math camps and universities around the world.

The connection between the pig and math might seem random, but that is kind of the point. Mathematics can feel rigid and intimidating, and Yellow Pig Day exists to inject some playfulness into the subject. It reminds people that math does not have to be all formulas and problem sets - sometimes it can be about a fictional pig with an oddly specific number of body parts.

Why the Number 17?

So what is so special about 17? Mathematicians have long found it interesting for several reasons. It is a prime number, meaning it can only be divided by 1 and itself. It is the sum of the first four prime numbers (2 + 3 + 5 + 7 = 17). It is also the only prime that is the average of two consecutive primes (it sits between 13 and 19, and sure enough, their average is 16... well, almost). In surveys where people are asked to pick a "random" number between 1 and 20, 17 comes up disproportionately often. There is something about it that just feels right to people.

Spivak and Kelly catalogued over 100 interesting properties of 17, turning their obsession into a legitimate mathematical tradition. The yellow pig became the mascot for this number, and the holiday gave everyone an excuse to celebrate the quirkier side of numbers.

How Yellow Pig Day Is Celebrated

At Hampshire College Summer Studies in Mathematics (HCSSiM), Yellow Pig Day has been a major event for decades. Students sing "Yellow Pig carols," share 17-themed puzzles, and eat yellow cake. Some participants dress in yellow, and there are even yellow pig stuffed animals that have become collector items among math camp alumni.

Beyond the academic world, the holiday has spread to social media where people share fun facts about 17, post yellow pig drawings, and use #YellowPigDay to connect with fellow math enthusiasts. Teachers use it as a hook to get students interested in number theory and mathematical curiosity.

How to Use #YellowPigDay on Social Media

This is one of those hashtags where creativity wins. Share a drawing of a yellow pig, post a mind-blowing fact about the number 17, or challenge your followers to find 17 in their daily lives. Math teachers can create classroom activities around it. Food bloggers can make yellow-themed treats with 17 ingredients. The hashtag works best when you lean into the absurdity - the more playful your content, the more engagement you will get.

Pair #YellowPigDay with #NationalYellowPigDay, #MathFun, #NumberTheory, or #MathTwitter to reach wider audiences. If you are posting on July 17th, the timing is perfect for maximum visibility.

Content Ideas for Brands and Creators

For brands looking to join the fun, consider running a "17 things" themed post - 17 facts about your product, 17 behind-the-scenes photos, or a 17-percent discount. Educational content creators can make videos explaining why 17 is mathematically interesting. Artists can create their own interpretation of the yellow pig. The key is to keep it lighthearted and not overthink the connection. People engage with this holiday because it is silly and unexpected, so match that energy in your content.