In the states it's quite common to number the floors of a building by avoiding the number 13. I think this is pure madness. 10, 11, 12, 14, 15...
All of that because of a fantasy book where people had supper and they happen to be 13 at the table.
Edit: Here's an example: https://en.wikipedia.org/wiki/13_(number)#/media/File:Many_b...