## Yellow Pig Day

Today is a special day for me … as I get to commemorate three of favourite themes … trivia, maths in several of its guises, and the calendar. You see, today is 17th July … and that means it’s **Yellow Pig Day**.

… and, yes, I can already hear the exasperated cries of **What?!**

Actually, it’s also World Emoji Day … but that’s another story … Yellow Pigs are much more interesting … although, I am pretty sure that not everyone will share my interest in the day …

Still, it’s my blog and I get to choose the topics(!)

It all started back in the 1960’s, when two Maths students from Princeton, (Michael Spivak and David Kelly), were given an assignment – nothing to do with pigs, yellow or otherwise – but to analyse the qualities and characteristics of the number 17.

They both went on to become Mathematics professors and carve out successful careers for themselves, despite, (or in spite of), being the originators of Yellow Pigs Day.

Why Seventeen? – well, that’s a good question … I am sure that people can think of far more interesting numbers …

- the one that immediately jumps into my mind is
– thanks to Douglas Adams and the Hitchhiker’s Guide to the Universe …**42** - but then there is always the five magical mysterious mathematical constants:
- Zero (
**0**), - one, (
**1**), - the square root of minus one (
),**i** - Euler’s number or the base of natural logarithms (
),**e** - Pi (
) – or for that matter Tau (**π**) –**τ**

- Zero (
- not forgetting ten (
), the basis of our number system**10** - twelve (
)**12** - mystical numbers like three (
), seven (**3**) and forty (**7**)**40** - Ramanjuman’s taxi number (
– … actually it was Hardy’s Taxi, but Ramanjuman who noticed that it was an interesting number) …**1729** - Münchhausen numbers like
**3435** - … and so on.

… and it is quite an interesting number … it would be interesting to see how many different innovative ways the twenty circles on an **Amazing Race** sheet for the number 17 could be filled in:

- a
number;**natural** - a
number;**positive** - a whole number (an
);**integer** - on
number;**odd** - a
number, (and not just a Prime number … an**prime**prime, a**Eisenstein**Prime, a**Fermat**, a**Mersenne prime exponent**Prime, and a**Proth**Prime…);**Stern** - there are 17
in plane geometry;**wallpaper groups** - you need a minimum of 17 clues in a games of
to guarantee a unique solution;**Sudoku** - it’s a
number;**Perrin** - a
number (and the only one that is also Prime … apart from -3, but that’s negative);**Gennoci** - it’s the ‘
‘ (at least in the in the set of integers from 0 to 20), now that one is**least random number***really*‘scary’ - … and so on …

… OK – I admit that I had to go and look some of those up … but that is also without the multitude of cultural and other significant factors, (in books, films, music, labels – like postal districts, roads, language peculiarities and so forth).

In Italy, 17 is the unlucky number – rather like 13 in the rest of the world … well, the English speaking world that is (and supposedly to do with the number of people at the last supper) and 4 in China (where the word for the number 4 is similar to the word for Death … similarly, In Roman numerals 17 is written as XVII – an anagram of VIXI – “I lived” – implying “My life is over”) …

If in China many buildings do not have a fourth floor, on AlItalia planes there is no 17th row.

It seems that the two students got so wound up in the assignment that, (one story has it over a pint of beer … and another that they were joking about Kelly’s collection of yellow pigs – plastic, ceramic, paper … people do collect the amazing things: teddy bears, elephants, plastic gnomes … and, apparently, yellow pigs), they invented a yellow pig with 17 toes, 17 eyelashes, 17 teeth … and so on.

The yellow pig became a sort of unofficial mascot for the *Hampshire College Summer Studies in Mathematics *(HCSSiM – a six-week program for mathematically talented high school students) which Kelly established in 1971 … it was formerly adopted in 2006 for the 34th Summer School, (34 = 2 x 17) and each year the students bake special cakes, make posters, design T-shirts, compose and sing Yellow Pig Carols … (Honest!) … andf give each other presents to commemorate the day at a reunion held on July 17th each year.

Oh, yes, and Kelly gives a lecture on the properties of the number 17 each year.

Spivak also maintains his connection to Yellow Pigs … he is a prolific author … and in each of his books there are references to Yellow Pigs …

One of his books, **Calculus on Manifolds**, (“a modern approach to classical theorems of advanced calculus”, as far as I can tell written in 1965 and published in 1968), is reputed to be (supposedly) one of the most difficult University Mathematics textbooks that students have to study …

I understood the first paragraph … and then got lost …

… and that is despite its brevity – in one version that I have seen, it’s just 42 pages long, (… Douglas Adams fans, take note).

To be honest … I did try to find a Kyrgyz connection for this postcard … but I failed:

- Yellow does not seem have any special significance;
- because most of the Kyrgyz are nominally Muslim, pigs are not really kept;
- and 17 doesn’t appear to be a special number to the Kyrgyz …

unless, that is, someone out there can enlighten me to the contrary.