The fear of numbers is arithmophobia. This fear is somewhat unusual in that it encompasses a wide variety of specific phobias. A generalized fear of numbers can affect the ability to do math, limiting both school performance and job opportunities. The fear of particularly large numbers is usually much less limiting, allowing sufferers to perform basic computations.
Arithmophobia also includes fears of specific numbers. These fears are often rooted in superstition or religious phobias, and deal with numbers that are held to have special powers. Fears of the numbers 13 and 666 are particularly common in the United States. Many hotels omit the 13th floor and the room number 13. Former President Ronald Reagan had the street number of his home in Bel-Air, Los Angeles, changed from 666 to 668. The fear of Friday the 13th combines the fear of Friday as an unlucky day with the fear of the number 13.Source:
American Psychiatric Association. (1994). Diagnostic and statistical manual of mental disorders (4th Ed.). Washington, DC: Author.