Triskaidekaphobia

noun

The fear of the number thirteen, and the reason a building may contain a thirteenth floor while refusing to name it.

Also known as fear of thirteen

Chapter 13. The Floor That Wasn’t There

A worn cream metal card-index box, open, with alphabetical tabs and a typed card at the front defining triskaidekaphobia: the fear or superstition surrounding the number thirteen. — Seek, and ye shall find.

Triskaidekaphobia is the fear or superstition surrounding the number thirteen, often associated with bad luck or misfortune in various cultures and individuals.

It is the reason buildings skip a floor, and the reason this site has a chapter that is not printed in the book. The lift panel knows how to count. It also knows people.