13 November: 13

10 things you didn't know about the number 13.

1. It's the atomic number of Aluminium.
2. In maths, it's the smallest emirp number, that is, a prime number which, when its digits are reversed, is also a prime number (ie 13 and 31.)
3. In the Jewish faith it is the age at which a boy comes of age and celebrates his Bar Mitzvah. It's also the minimum age to create accounts on a number of social media sites. In Germanic languages, it's seen as the age at which a child becomes a teenager, since it's the first compound number. 11 and 12 have their own names. This isn't the case in other languages however. In some, 11 is the first compound number and in others it's 17.
4. In the Tarot deck, card XIII is the card of Death; in Wicca, most covens have 13 members (though this is more likely to be to do with the 13 lunar months than any effort to be dark or sinister).
5. Could that be why 13 is considered unlucky in some countries? Perhaps, although there are other theories as to why this should be including that there were 13 people around the table at the Last Supper, the Knights Templar were massacred by King Philip IV of France on Friday 13 October 1307 and that a year with 13 full moons in it instead of 12 was problematic for monks who were in charge of calendars and setting dates for festivals.
6. Triskaidekaphobia, a word coined in 1911, is the fear of the number thirteen. Companies have a history of pandering to people with this phobia, which is why there is often no 13th floor in hotels or a row 13 on an aeroplane. NASA didn't avoid the number. There may have been a time when it wished it did: Apollo 13 was a mission famous for being a "successful failure" in 1970.
7. 13 isn't unlucky for everyone. Not all countries see it as unlucky. In Italy, 17 is the unlucky number. Singer-songwriter Taylor Swift was born on December 13 and considers 13 her lucky number because she's come to associate it with lucky events like her first album going gold in 13 weeks, being seated at awards shows in the 13th seat, row or section. She wears the number written on her hand at her concerts so she has it with her everywhere she goes.
8. Thirteen has come to be known as a baker's dozen, from times when a baker would include an extra loaf in orders of 12.
9. 15 is a significant number for the USA. It was created from thirteen British colonies, and this number occurs in its symbolism several times. There are 13 stripes on the Flag, 13 stars on the great seal. Also on the seal, the chest shield in front of the spread eagle bears thirteen stripes (seven White and six Red). In the eagle’s right talon, it holds the Olive Branch of Peace, bearing thirteen Olives and thirteen olive leaves. In the eagle’s left talon, it holds the Weapons of War, consisting of thirteen arrows. In the eagle’s mouth, it holds a scroll bearing the national motto “E Pluribus Unum” (which, by coincidence, consists of thirteen letters). On the back of the seal is an unfinished pyramid with 13 levels.
10. In rugby league, each side has 13 players on the field at any given time. Jersey number 13 is usually worn by the starting loose forward or lock forward. In rugby union, the jersey number 13 is worn by the outside centre.