Tridecaphobia: The fear of the number 13
Many buildings avoid numbering the 13th floor, while hotels avoid the number 13 room. Sport players do not wear shirts labeling the number 13, because they fear that the number may cause them to lose the game. Friday the thirteenth is considered the unluckiest day.
In the bible, the number 13 is the number of parties at the Last Supper. Jesus had the last supper with his twelve disciples and one of them betrayed him. He was arrested and crucified on the cross the next day.