(related to Part: Oddities and Curiosities)
The tongue twister triskaidekaphobia is the name of a fear of the number 13 and avoidance to use it. It stems from Greek "tris" meaning "3", "kai" meaning "and", "deka" meaning "10" and "phobos" meaning "fear" or "morbid fear".
People suffering from triskaidekaphobia in particular feel scared if they realize it's Friday the 13th. Unfortunately, in the Gregorian Calendar, the 13-th day of the month most offen falls on Fridays. The Gregorian Calendar repeats every 400 years (or 4800 months) in the sense that the same weekdays fall on the same days in all months of the year. During this cycle, the 13-th day of the month is