Yellow Pig Day is a holiday celebrated by mathematicians in a number of institutions.
The holiday began in the early 1960s in Princeton University when mathematicians Michael Spivak and David C. Kelly began looking at properties of the number 17. The fascination for the number eventually evolved into a yellow pig with 17 eyelashes and Yellow Pig Day was born.
July 17 marks the math holiday that began in Princeton and evolved in Hampshire College Summer Studies in Mathematics (HCSSiM), a high-school math program run in the summer by Kelley. Yellow Pig Day is marked by games of Ultimate, math-themed shirts with yellow pigs and origami yellow pigs.
The day is highlighted by a lecture from Kelley on the number 17. Students and faculty also sing Yellow Pig Day carols, exchange gifts related to the day and eat a yellow pig cake.