So I didn’t like my posts showing i’ve written 666 posts, so i’ll add another one. This one will do with #13.
If you look on a building and you see a floor that is all mechnical equipment. Usually the floor with no windows but all dark louvers, it is really easy to tell where it is at without even counting. 13th Floor
Same with doors, 13th door is usually the janitors closet or electrical room, so it has a different name and number.