13

The fear of number 13 is called triskaidekaphobia and it was derived from treiskaideka, the Greek word for thirteen and phobia. There were thirteen people at Christ's Last Supper before his captivity, it is recorder that Christ was crucified on Friday. Routine mission to the moon goes drastically wrong on Apollo 13. Some hotels skip number thirteen when numbering rooms. In Formula 1, there is no car with the number 13.

From: http://www.interestingfacts.org/?page=fact&id=45