Yellow Pigs Day is observed worldwide every July 17, primarily celebrated by mathematicians and math enthusiasts. The holiday originated at the Hampshire College Summer Studies in Mathematics (HCSSiM) program, founded by David C. Kelly in 1971, to honor the unique properties of the prime number 17. The celebration features the yellow pig, a mascot associated with HCSSiM, which symbolizes the number 17 and its characteristics, such as having 17 toes, teeth, and eyelashes. Alumni of the program return to campus for traditional festivities that include cake and Yellow Pig carols from the HCSSiM Yellow Pig Songbook. The day also serves as an opportunity for non-mathematicians to learn about the number 17 through lectures. Notably, July 17 has historical significance, as events like the premiere of Handel’s Water Music in 1717 and the Apollo-Soyuz mission in 1975 occurred on this date.