13

recently i found out that in USA and Canada the 13th floor is missing from many high rise buildings.
13 is considered an unlucky number [since it is a highly composite number?] and although architects/ owners are not [often] superstitious they have to skip floor 13 due to low rentability of this floor.
sometimes they rename the floor 12A or they give to the floor another function [ex. mechanical equipment etc].
in asia 4 is considered to be an unlucky number due to its death meaning. so they have similar policies for 4.14. 24 etc.

FYI*
triskaidekaphobia
thirteen floor

life of an architect is such a complicated life sometimes...