Heptadecaphobia (Greek: δεκαεπτάdekaepta, "seventeen" and φόβος, phobos, "fear") or heptadekaphobia is the fear of the number 17. It is considered to be ill-fated in Italy and other countries of Greek and Latin origins, while the date Friday the 17th is considered especially unfortunate in Italy. The number is feared due to superstition, and is similar in nature to the fear of the number 13inAnglo-Saxon countries.
InAncient Greece, the number 17 was despised by followers of Pythagoras, as the number was between 16 and 18, which were perfect representations of 4×4 and 3×6 quadrilaterals, respectively.[1]
It has been suggested that the Romans found the number 17 disturbing because in Roman numerals XVII is an anagram of vixi, meaning "I have lived" (i.e. I am dead).[3]
InLa smorfia napoletana, a "dictionary" that associated certain vocabulary words to numbers to be played in the lottery, the number 17 is associated with 'a Disgrazzia ("misfortune").[4]
In Italy, Friday the 17th (friggaheptadekaphobia or paraskevidekaeftaphobia[citation needed]) is a date of misfortune, as it is a date of two negatives: Friday (from Good Friday, the day of Jesus' death) and the number 17.[5] It occurs when the 17th day of the month in the Gregorian calendar falls on a Friday, which happens at least once every year but can occur up to three times in the same year. For example, 2017 and 2023 have a Friday the 17th in February, March, and November, which also happened thrice in January, April, and July in 2020; 2015, 2021, and 2025 through 2028 have two Friday the 17ths; 2016, 2018, 2019, and 2022 had just one Friday the 17th, as will 2024. [6]
Friday the 17th is similar to other unfortunate dates: for example, in Anglo-Saxon countries, this date is Friday the 13th, while in Spain, Greece, and South America, this date is Tuesday the 13th.
