n. The fear of the number 666.
Other Forms
A high school cross country runner in Kentucky didn't run in the regional meet on Saturday because she was assigned the number 666, which some Christians associate with evil….

Interpretation of the [Book of Revelations] has broadened to 666 being associated with the Anti-Christ or Satan. The association has become so common that a word, "hexakosioihexekontahexaphobia," has been coined to describe cases such as Thacker's in which people seek to avoid the number 666.
—Scott Douglas, “Teen Skips Meet After Getting Race Number 666,” Runner's World, November 06, 2013
The hotel henceforth provided a flunkey to eat with guests when they numbered 13, should they be haunted by triskaidekaphobia; but the guests didn’t like a flunkey, which was too like a chicken that spoke. (Didn’t the Savoy know that hexakosioihexekontahexaphobia is by far the smarter anxiety?)
—Tanya Gold, “Restaurant: Kaspar’s at the Savoy,” The Spectator, June 15, 2013
2005 (earliest)
Fear of the number actually has a name: Hexakosioihexekontahexaphobia, and it is surprisingly widespread:

Last year, Highway 666 in New Mexico, known as "the devil's highway," was renamed Highway 491. The governor of New Mexico lobbied for the name change because of its "negative connotations."
—Jenni Lee Campbell, “Bad omen: Mark of the beast is wrong, expert says,” Ottawa Citizen, May 03, 2005
This several mouthfuls of a word combines the Greek roots hexakosioi ("six hundred"), hexekonta ("sixty"), and hex ("six"). It's also, at 29 letters, by far the longest single-word entry in the Word Spy database. (The previous record holders, at a mere 23 letters, being deconstitutionalization and paraskevidekatriaphobia. Question: Is there a word for the fear of trying to pronouce this word in public?