- Any month’s 13th day will fall on a Friday if the month starts on Sunday.
- The fear of Friday the 13th is called friggatriskaidekaphobia (Frigga being the name of the Norse goddess for whom “Friday” is named and triskaidekaphobia meaning fear of the number thirteen).
- According to folklorists, there is no written evidence for a “Friday the 13th” superstition before the 19th century. The first reference occurs in Henry Sutherland Edwards’ 1869 biography of Gioachino Rossini.
- In numerology, the number 12 is considered the number of completeness, as reflected in the 12 months of the year, 12 hours of the clock, 12 gods of Olympus, 12 tribes of Israel, 12 Apostles of Jesus, the 12 Descendants of Muhammad Imams, etc., whereas the number 13 was considered irregular, transgressing this completeness.
— Source: en.wikipedia.org