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Pi Day is a cheeky celebration of the mathematical constant found by dividing a circle’s circumference by its diameter, which is 3.14 when rounded to two decimal points. If you have any friends or coworkers who want to show off their mastery of fifth-grade geometry and sixth-grade home economics, you may even get a home-baked pie out of it. But what about those of us with an appetite for math holidays that find celebrations of constants to be a bit too predictable?

## Fibonacci Day (Nov. 23)

Every number in the Fibonacci sequence is the sum of the two numbers before it. If you were to add 1 and 1, you’d get 2; if you then added 1 and 2, you’d get 3, which is why Nov. 23 is the most appropriate day to celebrate the Italian mathematician Fibonacci’s titular contribution to his field. How to mark the occasion? We suggest a Fibonacci potluck: Every contribution to the meal must be quantified by the sum of the two contributions before it.

Say Adam brings a salami and Sally brings a wooden board. That’s one lame sausage fest of a party! But if Molly brings two bottles of wine, Jasper brings three blocks of cheese and Dakota brings five dinner rolls, now you’ve got yourself a little Fibonacci antipasto.

## Hilbert Day (Feb. 3)

German mathematician David Hilbert had a bunch of complicated problems—23, to be exact, hence the date—and he wanted somebody else to solve them. Can’t you relate? Give the guy a holiday! Hilbert’s problems helped to shape the direction of mathematical study throughout the 20th century, although there are differing claims about which have been definitively resolved. However, several theorems were developed throughout the last century that satisfactorily address the problems, such as Matiyasevich’s theorem, which combines computability theory and number theory, and the Gelfond-Schneider theorem, which established that any algebraic number other than 0 or 1 squared by an irrational number is a transcendental number.

Hilbert Day should inspire us to search for answers, but to embrace the unknown and ambiguous. To fete Hilbert, celebrants must eat a ripe tomato in recognition of the plant’s dual identity as a fruit (according to botanists) and a vegetable (according to everyone else). Existing in this liminal space reflects the pleasure and pain of doing mathematical proofs.

## Pythagorean Day (Dec. 16, 2020)

You’ll have more than enough time to prepare for this last holiday, when the sum of the month and day squared equals the last two numbers of the year squared. Any diehard math fan has probably had an awkward moment where they knew the lengths of two sides of a right triangle, but not the third. Thankfully, Greek mathematician Pythagoras has had us covered since around 500 BC with his theorem: you can calculate the length of a right triangle’s hypotenuse by finding the square root of the sum of the square values of its other two lengths.

To celebrate Pythagorean Day, it’s all things triangles: cut your sandwich diagonally, eat a slice of pizza, or treat the gang to samosas—just stay away from circles at all costs!