The number thirteen has long held a special attraction. Thirteen is a prime number, a Fibonacci number, and a happy number (calculated for any positive integer as the sum of the squares of its digits, repeated until the process either equals one [a happy number] or endlessly loops [unhappy number]).
Thirteen is the age in Judaism in which a boy becomes a man and full member of the Jewish faith through the Bar Mitzvah. A thirteenth anniversary is called a tredecennial(1) or tridecennary(2) (tridecennary can also apply to a period of thirteen years). A triskaidecago(3) is a polygon with thirteen sides (also called a tridecagon(4)). A clutch(5) is a unit of count equal to thirteen (typically concerning eggs), and a devil’s dozen(6) may also refer to a count of thirteen. And the thirteen offsprings of a single birthing are known as tredecaplets(7).
Thirteen also has many sinister meanings, such as the number of witches in a coven(8), and Sizdah Be-dar, the thirteenth day of the Zoroastrian new year which is held to be a day in which evil exerted great power and people traditionally retreated to countryside in an effort to avoid any ill effects commonly associated with life in urban areas. And XIII is the tarot card of death.
We more famously associate the fifteenth of the month with the ancient Roman term ides, because of Caesar’s famous run-in at the Senate on the ides of March (March 15th), but on only four months of the year did the ides fall on the fifteenth; on the other eight months they fell on the thirteenth, so the unlucky connotation of ides is associated with both the numbers 15 and 13.
Over the years, the number thirteen has increasingly become associated with ill luck. So much so, there’s even a word (actually two) for the morbid fear of the number thirteen: triskaidekaphobia(9) or tridecaphobia(10). There’s a number of theories for how thirteen came upon this unfortunate reputation, but the true reason isn’t actually known. Some believe it relates to the thirteen attendees at Jesus’ Last Supper, the thirteenth being Judas Iscariot who betrayed Christ. Also, some years have thirteen full moon cycles (about one-third do), instead of the usual twelve, which was considered unlucky because it upset the timing of certain religious moveable feasts, such as Easter (see https://thewordmaven.wordpress.com/2009/04/12/easter/). Some people even believe the tradition of considering thirteen as unlucky goes all the way back to the Babylonian Code of Hammurabi, dating around 1780 BC, in which the thirteenth code deals with circumstances associated with an individual’s death.
And of course, Friday the thirteenth has its own tradition as a luckless time. There’s even a term for the fear of this auspicious day: paraskevidekatriaphobia(11).
On a lighter note, back around 1266 in England, Henry III revived a statute regulating the price of bread based on the weight of a standard loaf. In tough economic times or in times of bread shortages, bakers were known to shirk the law by baking smaller loaves. This was illegal and some bakers ended up in the goal or publicly flogged for their illicit behavior. So the story goes that bakers began adding a little extra slice to each loaf, and a full extra loaf to orders of a dozen loaves. The thinking was that this practice would offset any inadvertent shortage of weight. As you have probably guessed, this tradition became known as a baker’s dozen(12), or thirteen for the price of twelve. And a little word trivia−the thirteenth item in a baker’s dozen is known as the advantage.
In a similar vein, any unexpected free gift received with purchase is now known by several terms: brotus, pilon (from the Southwest U.S.), and from Louisianna we get lagniappe (also spelled lagnappe) which can also mean a bribe or a tip. I can remember merchants doing this a lot more when I was growing up than they do now, but maybe free shipping is today’s rough version of a brotus.
Falling somewhere between a baker’s dozen and a brotus is a poulter’s measure. Beginning at least several centuries ago, poulters (those who farm poultry) began the practice of giving away two additional eggs for every second dozen ordered. So, the first dozen ordered brought you twelve eggs and the second, fourteen. It doesn’t take a genius to figure out that the average was thirteen but the extra amount wasn’t added on until that extra order. This is like a baker’s dozen with a catch. At some point, a type of poem having alternate lines of verse consisting of twelve and fourteen syllables also became known a poulter’s measure.
Italians seem to buck the trend and consider thirteen as a lucky number, where fare tredici (13) (literally, “to do 13”) means to hit the jackpot.
Regardless of whether you are superstitious, prudently cautious, or one of those willing to throw caution to the wind and embrace all numbers as equals, thirteen has a rich and proud history. But I would definitely urge caution when purchasing a dozen donuts if the ides of January, February, April, June, August, September, November, or December fall on Friday the thirteenth of the tredecennial of your thirteenth birthday.