Triskaidekaphobia

Triskaidekaphobia is fear or avoidance of the number. It is also a reason for the fear of Friday the 13th, called paraskevidekatriaphobia or friggatriskaidekaphobia.
The term was used as early as in 1910 by Isador Coriat in Abnormal Psychology.

Origins

The supposed unlucky nature of the number 13 has several theories of origin. Although several authors claim it is an older belief, no such evidence has been documented so far. In fact, the earliest attestation of 13 being unlucky is first found after the Middle Ages in Europe.

Playing cards

have been attested since at least around 1450 with the Visconti-Sforza Tarot. One of the trump cards in tarot represents Death, and is numbered 13 in several variants.
In 1781, Antoine Court de Gébelin writes of this card's presence in the Tarot of Marseilles that the number thirteen was "toujours regarde comme malheureux". In 1784, Johann Gottlob Immanuel Breitkopf cites Gébelin, and reaffirms that the tarot card number 13 is death and misfortune.

13 at a table

Since at least 1774, a superstition of "thirteen at a table" has been documented: if 13 people sit at a table, then one of them must die within a year. The origin of the superstition is unclear and various theories of its source have been presented over the years.
In 1774, Johann August Ephraim Götze speculated:

Da ich aus der Erfahrung weis, daß der Aberglaube nichts liebers, als Religionssachen, zu seinen Beweisen macht; so glaube ich bey nahe nicht zu irren, wenn ich den Ursprung des Gegenwärtigen mit der Zahl XIII, von der Stelle des Evangelii herleite, wo der Heiland, bey der Ostermahlzeit, mit zwölf Jüngern zu Tische saß.

Since I know from experience that superstition loves nothing better than religious matters as its proofs, I believe I'm almost certainly unmistaken when I derive the origin of the matter of the number XIII from the passage of the Gospel where the Savior sat at table with twelve disciples at the Easter meal.

From the 1890s, a number of English-language sources reiterated the idea that at the Last Supper, Judas, the disciple who betrayed Jesus, was the 13th to sit at the table. The Bible says nothing about the order in which the Apostles sat, but there were thirteen people at the table.
In 1968, Douglas Hill in Magic and Superstition recounts a Norse myth about 12 gods having a dinner party in Valhalla. The trickster god Loki, who was not invited, arrived as the 13th guest, and arranged for Höðr to shoot Balder with a mistletoe-tipped arrow. This story was also echoed in Holiday Folklore, Phobias and Fun by folklore historian Donald Dossey, citing Hill. However, in the Prose Edda by Snorri Sturluson, the story about Loki and Balder does not emphasize that there are 12 gods, nor does it talk about a dinner party or the number 13.

Events related to "unlucky" 13

On Friday, October 13, 1307, the arrest of the Knights Templar was ordered by Philip IV of France. While the number 13 was considered unlucky, Friday the 13th was not considered unlucky at the time. The incorrect idea that their arrest was related to the phobias surrounding Friday the 13th was invented early in the 21st century and popularized by the novel The Da Vinci Code.
In 1881, an influential group of New Yorkers, led by US Civil War veteran Captain William Fowler, came together to put an end to this and other superstitions. They formed a dinner cabaret club, which they called the Thirteen Club. At the first meeting, on January 13, 1881, at 8:13 p.m., thirteen people sat down to dine in Room 13 of the venue. The guests walked under a ladder to enter the room and were seated among piles of spilled salt. Many "Thirteen Clubs" sprang up all over North America over the next 45 years. Their activities were regularly reported in leading newspapers, and their numbers included five future US presidents, from Chester A. Arthur to Theodore Roosevelt. Thirteen Clubs had various imitators, but they all gradually faded due to a lack of interest.
The British submarine sank on 29 January 1917 while on her trials after diving with a hatch and some vents still open. Although she was raised and 48 men were rescued, 32 sailors and civilian technicians died. When repaired, she was renamed K22 but was later involved in multiple collisions with other K-class submarines on 1 February 1918 in which a total of 103 men were killed, an event known as the Battle of May Island. In the subsequent British L-class submarine, the number L13 was not used.
Apollo 13 was launched on April 11, 1970, at 13:13:00 CST and suffered an oxygen tank explosion on April 13 at 21:07:53 CST, forcing it to abort its mission to land on the Moon. All crew returned safely to Earth on April 17.
The Friday the 13th mini-crash was a stock market crash that occurred on Friday, October 13, 1989.
Vehicle registration plates in Ireland are such that the first two digits represent the year of registration of the vehicle. In 2012, there were concerns among members of the Society of the Irish Motor Industry that the prospect of having "13" registered vehicles might discourage motorists from buying new cars because of superstition surrounding the number thirteen, and that car sales and the motor industry would suffer as a result. The government, in consultation with SIMI, introduced a system whereby 2013 registered vehicles would have their registration plates' age identifier string modified to read "131" for vehicles registered in the first six months of 2013 and "132" for those registered in the latter six months of the year.
Effect on US Shuttle program mission naming

The disaster that occurred on Apollo 13 may have been a factor that led to a renaming that prevented a mission called STS-13. STS-41-G was the name of the thirteenth Space Shuttle flight. However, originally STS-41-C was the mission originally numbered STS-13. STS-41-C was the eleventh orbital flight of the space shuttle program.
The numbering system of the Space Shuttle was changed to a new one after STS-9. The new naming scheme started with STS-41B, the previous mission was STS-9, and the thirteenth mission would be STS-41C. The new scheme had first number stand for the U.S. fiscal year, the next number was a launch site, and the next was the number of the mission numbered with a letter for that period.
In the case of the actual 13th flight, the crew was apparently not superstitious and made a humorous mission patch that had a black cat on it. Also, that mission re-entered and landed on Friday the 13th which one crew described as being "pretty cool". Because of the way the designations and launch manifest work, the mission numbered STS-13 might not have actually been the 13th to launch as was common throughout the shuttle program; indeed it turned out to be the eleventh. One of the reasons for this was when a launch had to be scrubbed, which delayed its mission.
In a 2016 news article, NASA stated that the numbering system change was due to a much higher frequency of planned launches. As it was, the Shuttle program did have a disaster on its one-hundred and thirteenth mission going by date of launch, which was STS-107. The actual mission STS-113 was successful, and had actually launched earlier due to the nature of the launch manifest.

Omission of 13th rooms

Hotels, buildings and elevator manufacturers have also avoided using the number 13 for rooms and floors based on triskaidekaphobia.
Several notable streets in London lack a No. 13, including "Fleet Street, Park Lane, Oxford Street, Praed Street, St. James's Street, Haymarket and Grosvenor Street."

Thirteenth floor

The thirteenth floor is a designation of a level of a multi-level building that is often omitted in countries where the number is considered unlucky. Omitting the 13th floor may take a variety of forms; the most common include denoting what would otherwise be considered the thirteenth floor as level 14, giving the thirteenth floor an alternative designation such as "12A" or "M", or closing the 13th floor to public occupancy or access.
Reasons for omitting a thirteenth floor include triskaidekaphobia on the part of the building's owner or builder, or a desire by the building owner or landlord to prevent problems that may arise with superstitious tenants, occupants, or customers. In 2002, based on an internal review of records, Dilip Rangnekar of Otis Elevators estimated that 85% of the buildings with at least thirteen floors with Otis brand elevators did not have a floor named the 13th floor. Early tall-building designers, fearing a fire on the 13th floor, or fearing tenants' superstitions about the rumor, decided to omit having a 13th floor listed on their elevator numbering. This practice became commonplace, and eventually found its way into American mainstream culture and building design.
Vancouver city planners have banned the practice of skipping 4s and 13s, since it could lead to mistakes by first responders, such as going to the wrong floor in an emergency.

Origin

The origin of skipping the thirteenth floor when installing elevators is not known. However, during the advent of early skyscrapers, New York architectural critics warned developers not to exceed the height of the 13th floor. These critics insisted that buildings rising above the 13th floor would lead to increased street congestion, ominous shadows and lower property values. Nevertheless, in a work published in 1939, sociologist Otto Neurath compared the use of money in an economy, which he saw as unnecessary, to the superstition of not installing the thirteenth floor: merely a social convention.

Methods of avoiding

Skipping: Most commonly, 13 is skipped, as in: 12, 14, 15... The floor labeled "14" on the elevator is the thirteenth floor and the number 13 is skipped on the elevator console. In such buildings, floors after 12 are nominally incorrect, with their labeled floor being one higher than the actual floor. Many ships, including cruise liners have omitted having a 13th deck due to triskaidekaphobia. Instead, the decks are numbered up to 12 and skip straight to number 14.
12A, 12B, 14: Sometimes to keep numbers consistent the 13th floor is simply renumbered as 12A or 12B, as in: 12, 12A, 14.., or 12, 12B, 14; this does not affect the numbers of the higher floors. Likewise, 14 could be used for the 13th floor and 14A or 14B could be used for the 14th floor.
Special designations: Other buildings will often use names for certain floors to avoid giving a floor on the building the number 13 designation. One such example is the Radisson Hotel in Winnipeg, Manitoba, where the 13th floor is called the pool floor. Another example is the Sheraton on the Falls in Niagara Falls, Ontario, where the 13th floor consists solely of a restaurant. A third example is the Trump International Hotel and Tower Chicago in Chicago, Illinois, where the 13th floor is the mezzanine floor.
Uninhabited 13th floor: sometimes, the floor is put to some other use, such as a mechanical floor. Such usage is sometimes the subject of conspiracy theories.
Letter M: In Richmond, Virginia, the Monroe Park Towers has a 13th floor, but it is used for mechanical equipment and is only accessible from the freight elevator or the stairs. The M designation on the elevator buttons of the freight elevator can also be construed as meaning the Mechanical level in this particular building, or as a Mezzanine level.
Split-level apartments: Sometimes, a tenement block will contain split-level apartments where the units themselves contain internal staircases and the main elevators for the building therefore do not stop on every floor. One example is Princess Towers in Kingston, Ontario, which has stories excluding the roof-top. The elevators stop at B, G, 3, 6, 9, 12 and 15th floors only. In this case, the unmarked 11th and 13th floors are accessed within units on the marked 12th floor.