Posted
on July 17, 2014
I
love a math holiday, like Pi Day (3/14, because pi =
3.14...) or Mole Day (6:02 on 10/23, because Avogadro's Number is
6.02 * 10^23).
Today
is a math holiday! It celebrates the number 17, which is the seventh
prime number (hence 7/17). But what is the connection to yellow pigs,
you may ask?
In
the early 1960s, when holiday creators Michael Spivak and David C.
Kelly were students at Princeton University, majoring in math, they
began to list interesting properties of the number 17. Somehow, a
yellow pig with 17 eyelashes was born – and it's been a thing ever
since.
Okay,
that still sounds pretty random, doesn't it? But how does any
tradition start? How did the birth of a religious figure get
associated with a gentleman who lives at the North Pole? How did a
feast for Saint Patrick get associated with painting faces green and
pouring green coloring into rivers—even though St. Patrick's flag
is red and white?
At
any rate, for probably completely random reasons (or no reason),
Spivak and Kelly invented a yellow pig. Since then, Spivak has
written many famous math textbooks – and he has included yellow
pigs in them. Kelly runs a summer program for high school students
who are “into” math, and he has introduced them to the “cult”
of the Yellow Pig. Kelly has a collection of hundreds of yellow pigs, and a few
other mathematicians have been inspired to collect them, too.
For
more than three decades, mathematicians and math students have
celebrated Yellow Pig Day by wearing shirts decorated with yellow
pigs, playing a frisbee game called Ultimate, displaying collections
of yellow pigs and origami yellow pigs, singing Yellow Pig Day carols
(I kid you not), and eating a yellow pig cake. Some people exchange
yellow pigs and mathematical knick knacks and other gifts.
Of
course, the very best way to celebrate Yellow Pig Day is to learn
more about the number 17!
The
Number 17
17
is not only a prime number (which means that no two numbers
multiplied together equal 17 – other than 1 and 17 itself), but it
is the sum of the first four prime numbers:
2
+ 3 + 5 + 7 = 17
17
is the only known prime that is equal to the sum of the digits of its
cube:
17
* 17 * 17 = 4913
4
+ 9 + 1 + 3 = 17
17
is the only prime that is the average of two consecutive Fibonacci
numbers:
Fibonacci
numbers are the sum of each two previous numbers:
1,
1 - 1 + 1 = 2
1,
1, 2 - 1 + 2 = 3
1,
1, 2, 3 - 2 + 3 = 5
1,
1, 2, 3, 5 – 3 + 5 = 8
and
so on...
1,
1, 2, 3, 5, 8, 13, 21, 34, 55, 89...
13
+ 21 = 34
34
divided by 2 = 17
Also
on this date:
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