Triskaidekaphobia is the fear of the number thirteen. The number 13 has been linked to bad luck in the western superstition. Some buildings in the United States do not have a "13th floor."
The term was first used by Isador Coriat in Abnormal Psychology.
There is also a fear of Friday the 13th. This fear is called paraskevidekatriaphobia or friggatriskaidekaphobia.