at first i thought it would be an accident number in 1 of those countries. But that's not true.
wiki also had a nice picture The elevator in an apartment building in Shanghai, floors 0, 4, 13 and 14 are missing link
Many numbers used to have a symbolic meaning. We call the number 11 the mad number because it can only be divided by itself and because 11 stands between 10 (the perfect number) and 12 (the holy number). The number 11 is both an accident number (it breaks the perfect number 10) and a lucky number (it is twice 1: the symbol of concord).
That is why it is a “crazy” number. So it has nothing to do with elves, as some people think.
[Comment modified by No_mercy428 on February 14, 2020 7:52 AM]