Octadecagon

A octadecagon or 18-gon is a shape with 18 sides and 18 corners.

 Regular octadecagon 
All sides of a regular octadecagon are the same length. Each corner is 160°. All corners added together equal 2880°.

 Area 
The amount of space a regular octadecagon takes up is

The area of a regular octadecagon of side length a is given by

18