Do you know that in many buildings in South korea especially hospitals the elevators do not have a button for the fouth floor ,instead it is represented as the English letter F. It is because in korean culture the number 4 is considered to be bad luck . As the korean word for 4 sounds a lot like the korean word for death.

This fear of number 4 is know as Tetraphobia ( combination of greek words tetra - four and phobia - fear ) it is common in cultured of Japan and China as well.