Let <math>_p\mathrm{log}_gx</math> denote the discrete logarithm according to the prime number <math>p</math>, i.e., the number <math>l</math> modulo <math>p-1</math> such that
<math>g^x \equiv l \pmod{p}</math>
Then 13 is the only prime number <math>p</math> such that for any two primitive roots <math>g</math> and <math>h</math>,
The Saros number of the lunar eclipse series which began on -2313May 20 and ended on -1015July 6. The duration of Saros series 13 was 1298.1 years, and it contained 73 lunar eclipses.
In modern day Wicca, thirteen is considered the maximum size of a coven, and in some traditions is the ideal number of members, and there are also 13 goals of a witch.[1]
In Sikhism, the number thirteen (13) is a number devoted to the remembrance of God, therefore it is also considered lucky by people who practice the Sikh faith.
A Significant Number
For various reasons 13 is considered a number carrying a special significance in many cultures.
The stall numbers at the Santa Anita Park show that 13 is considered an unlucky number in horse racing.
Thirteen is regarded as an unlucky number in many cultures. Thirteen may be considered a "bad" number simply because it is one more than 12, which is a popularly used number in many cultures (possibly due to it being a highly composite number). When a group of 13 objects or persons is divided into two, three, four or six equal groups, there is always one leftover, "unlucky" object or person.
Unreasoned fear of the number 13 is termed triskaidekaphobia. Due to this fear, some tall buildings have resorted to skipping the "thirteenth floor", either by numbering it "14" (though it's really still the thirteenth floor) or by designating the floor as "12a" or something similar. Similarly, some streets do not contain a house number 13.
Some Christian traditions have it that at the Last Supper, Judas Iscariot, the disciple who betrayed Jesus, was the 13th to sit at the table, and that for this reason 13 is considered to carry a curse of sorts. However, there is evidence that 13 may have been considered unlucky in the pre-Christian era: the Code of Hammurabi, a collection of laws created ca. 1760 BCE, does not contain a thirteenth law.
According to another interpretation, the number 13 is unlucky because it is the number of full moons in a year. Actually two full moons in a single calendar month (referred to as a Blue Moon) only happens about every 2.5 years, so to say there are 13 full moons in a year is false. On average, there will be 41 months that have two full moons in a century, so a Blue Moon actually occurs about once every two-and-a-half years, and is in no way related to the number 13.[2] Women living in a natural environment tend to have their menses during a full moon.[citation needed] A twenty-eight day menstruation cycle is most typical, so a woman usually has 13 menses in a year. Supposedly, in the past, a woman who menstruated during a full moon might be thought a witch.
Early nursery rhymes stated there were thirteen months in a year because of the natural moon cycle that was used to count the lunar year. In England, a calendar of thirteen months of 28 days each, plus one extra day, known as "a year and a day" was still in use up to Tudor times. The lunar year was the easiest to count for cultures before scientific methods existed to observe the movement of the earth around the sun, so it was associated with worship of the pagan Great Goddess[citation needed] for thousands of years, which may be another reason for 13 becoming a taboo number. Taboo often is misunderstood when only half of the totem and taboo relationship is recognized. Among religions having totem and taboo characteristics, that which is taboo on a regular basis, may become quite sacred on special occasions.
The thirteenth of a month is likewise ominous, particularly when it falls on a Friday (see Friday the 13th), a Tuesday in the Greek and Spanish-speaking world, or a Monday in Russia. Months with a Friday the 13th must always begin on a Sunday.
In the Persian culture, 13 is also considered an unlucky number. On the 13th day of the Persian new year (Norouz), people consider staying at home unlucky, and go outside for a picnic in order to ward off the bad luck.
Most race car drivers consider 13 a very unlucky number, as a car carrying that number has never won the Indianapolis 500 or a NASCAR Nextel Cup race, and most all Formula 1 teams opt out of carrying the number 13 when car numbers are given out to teams on basis of points. Only once in recent years (1991, Ricky Johnson) has an AMA Motocross rider chosen #13 instead of #14. Some NASCAR tracks refuse to have a pit stall #13.
The career of Alex Rodriguez has taken a notable turn for the worse since donning the #13 for the New York Yankees.
In Tarot decks, the #13th card of the Major Arcana is Death (Tarot card). While Death is not typically interpreted literally, it is possible that this furthered the perception of 13 as an unlucky number.
Lucky 13
In Sikhism, the number 13 is considered a special number since 13 is tera in Punjabi, which also means "yours" (as in, "I am yours, O Lord"). The legend goes that when Guru Nanak Dev was taking stock of items as part of his employment with a village merchant, he counted from 1 to 13 (in Punjabi) as one does normally; and thereafter he would just repeat "tera", since all items were God's creation. The merchant confronted Guru Nanak about this, but found everything to be in order after the inventory was checked.
Several successful athletes have worn the number 13. Dan Marino, an American football player known for passing more yards than any other quarterback in NFL history, wore the number 13. Another athlete Wilt Chamberlain wore the number 13 on his jersey throughout his NBA career. Also, FIBA rules require a player to wear the number in international competitions (only numbers from 4 to 15 could be worn, and as there are 12 players, one must wear 13); Chris Mullin, who wore #20 in college and #17 in the NBA, wore #13 for both (1984 and 1992) of his Olympic appearances. Shaquille O'Neal wore #13 in 1996, Tim Duncan wore #13 in 2004. And Mats Sundin wears 13 in NHL.
In Judaism, 13 is considered a lucky number. One explanation for this is that the word אחד echad, Hebrew for 'one' and thus a way of describing the unique God, has the numerological value of 13 according to the Gematria system.
In mythology
The number of circles, or "nodes", that make up Metatron's Cube.
The number of Norse gods (there were 12) at a banquet that was crashed by the evil spirit Loki (making 13) who killed one of the guests with a poison arrow.
The number of steps, according to Egyptian lore, between life and death.
Age 13
In Jewish tradition a boy becomes a bar mitzvah at age 13, when a ceremony is held and the boy reads from the Torah for the first time.
On October 13th, 2000, the 13th birthday is on the 13th day in October (golden birthday) on a Friday and on the same day... a full moon.
A period of 13 years is called a tridecennary, although that word is hardly ever seen in print, and only appears in one dictionary, the Oxford English Dictionary.
In media
In music:
XIII (band) is a metalcore band from the Netherlands - Hoorn.
Golgo 13, an anime about a powerful hitman. The name comes from Golgotha, the site of Jesus's crucifixion.
13 Tzameti, a 2005 film by Géla Babluan. A film where the main character finds himself in a game of Russian Roulette and is assigned the number 13. In this case the number turns out to bring him luck.
"Thirteen Ways of Looking at a Blackbird" is a poem by Wallace Stevens.
In the episode of King of the Hill when Connie has her first period and she goes with Hank to the Megalomart to buy tampons, the feminine hygiene items are in Aisle 13. This was changed to Aisle 8A when the episode reran.
The thirteenth episode of the animatedTV programDanny Phantom is named, appropriately enough, "13" and centers around a bad luck charm.
A song by the band Osker, also the title of a song by the band Bigwig
Every book in A Series of Unfortunate Events has 13 chapters, and there are thirteen novels in that particular series, the last of which was released on Friday, October 13, 2006. This excludes the countless extra books, of which 2 are still in the process of being published.
The 13 Ghosts of Scooby Doo, an animated TV series where the venerable cartoon dog finds and opens a chest containing 13 of the most powerful ghouls in the world, and is charged with putting them back.
The number of apostles who divided Earth into Stark and Arcadia in the alternate universe of The Longest Journey as well as the time, in millennia, that the Balance between the twin worlds was projected to last.
In the manga Black Cat, the main character has a tattoo of the number 13 (XIII) on his chest with the same symbol engraved on his gun.
United States of America
The number of original colonies the United States was founded from. The original flag had thirteen stars, one for each state. New stars have since been added whenever a new state joins the union, but the idea of adding stripes for new states was soon dropped, so the American flag to this day has thirteen horizontal stripes: six white ones and seven red ones.
The expression, "A year and a day" refers to 13 28-day lunar months plus 1 day
The number of Popes named Innocent, for which an honor society containing 13 members at the University of Nebraska is named ("The Society of Innocents")
The number of cards in a single suit of a standard deck of playing cards
The number of Plutonium slugs in Fat Man, the atomic bomb dropped on Nagasaki
The number 13 on a Hells Angel's, Ton-Up or other biker patch or tattoo refers to the thirteenth letter of the alphabet, M, which signified a marijuana smoker.
13, or "X3", is the number of the Mexicanstreet gangSureños. It refers to the thirteenth letter of the alphabet, M, for Mexico
In rugby union one of the centres, most often but not always the outside centre, wears the 13 shirt
There are traditionally thirteen steps leading up to a gallows. It is, however, an urban myth that there are thirteen turns in a hangman's noose (there are most commonly eight turns.)
Colgate University, in New York State, has a certain liking for the number thirteen. The University was founded in 1819 by thirteen men, with thirteen dollars and thirteen prayers. Colgate is located in Hamilton, whose zip code, 13346, has both the number "13" in it, as well as its last three numbers adding up to thirteen.
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