13

Many tall buildings label the floor above the twelfth as fourteen. The floor exists and the number does not, which makes the practice a measurable record of how widely the belief is accommodated rather than held.

There are 13 letters in the Hawaiian alphabet (Hawaiian). Five vowels, seven consonants and the ʻokina, which marks a glottal stop and is a letter rather than punctuation.

There are 13 Wi-Fi channels available in the 2.4 gigahertz band (Europe, under ETSI rules). The United States allows 11 and Japan 14, so the same hardware is legal on different channels in different places. Only 1, 6 and 11 do not overlap, which is why those three are the ones worth choosing between.

The fuse rating of a standard British plug for a high-power appliance is 13 amperes (United Kingdom, BS 1363). 3 amp and 13 amp are the two common ratings, and the fuse protects the flex rather than the appliance. The British plug is fused at all because ring circuits carry a higher breaker rating than a flex can survive.

The word "triskaidekaphobia" itself is a relatively modern coinage (documented from the early 20th century), even though the underlying superstition draws on older, multi-causal sources — including the Last Supper's 13 diners (with Judas counted as the 13th) and earlier Norse mythology. The specific practice of omitting a labelled 13th floor is a documented 19th-to-20th-century Western building convention, not an ancient one. The association is also not universal even within Europe: Italy has a long-documented tradition treating 13 as a lucky number, historically linked to the Virgin Mary or Saint Anthony depending on the region — a genuine, well-attested counter-example that shows the fear is a specific cultural pattern, not a human universal.

In Jewish tradition a boy becomes bar mitzvah at 13, obligated to keep the commandments; the equivalent for girls, bat mitzvah, is at 12 in Orthodox practice and 13 in most Reform and Conservative communities. The status arrives with the age whether or not any ceremony is held.

The most commonly cited origin of thirteen's unlucky reputation in Christian-influenced cultures is the number present at the Last Supper. The association is traditional; the earliest clear written evidence of the superstition is far later than the event.

There are 13 or seventeen years between emergences of periodical cicadas (North America). Both are prime, which reduces the chance of synchronising with shorter predator cycles.

13 is the atomic number of aluminium, the most abundant metal in Earth's crust.

Triskaidekaphobia — fear or avoidance of the number 13 — is a well-documented Western cultural phenomenon; many hotels, hospitals and apartment buildings omit a labelled 13th floor, and some airlines omit row 13.

Thirteen is where the English word 'teenager' begins, since it is the first number ending in -teen. The category is a mid-twentieth-century coinage; the numbers it covers are an accident of English number words rather than anything about adolescence.

A superstition in much of Europe and the Americas holds that thirteen is treated as unlucky, and floors, rooms and seat rows are frequently numbered around it. Triskaidekaphobia has several proposed origins — the Last Supper, a Norse myth, the suppression of the Templars in 1307 — and none is established. The competing origins are better evidence of how such a belief accretes explanations than of where it came from. This is a scholarly account rather than the tradition's own framing.

Presented as belief or tradition, not as an established fact.

In aviation and hospitality, it is traditional that row 13 and floor 13 are routinely omitted from aircraft and buildings, so the numbering skips. A commercial response to a belief rather than the belief itself, and the two are worth separating: the airline is not superstitious, it is avoiding complaints. Several carriers also omit row 17, which is the unlucky number in Italy. This is a scholarly account rather than the tradition's own framing.

Presented as belief or tradition, not as an established fact.

A superstition in Spanish- and Greek-speaking countries holds that Tuesday the thirteenth rather than Friday the thirteenth is the unlucky date. Tuesday is named for Mars in the Romance languages, and Constantinople fell to the Fourth Crusade on a Tuesday. The English-speaking world's Friday is the local variant, not the standard one. This is a scholarly account rather than the tradition's own framing.

Presented as belief or tradition, not as an established fact.

The number of the amendment that abolished slavery is 13 (United States, ratified 1865). It abolished slavery and involuntary servitude except as punishment for a crime — an exception that remains in the text and is still litigated.