Icosagon

An icosagon is a shape with 20 sides and 20 corners. It has interior angles of 162 and exterior angles of 18.

 Regular icosagon 
The regular icosagon has Schläfli symbol {20}, and can also be constructed as a truncated decagon, t{10}, or a twice-truncated pentagon, tt{5}. 

 Area 
The amount of space a regular icosagon takes up is

a is the length of one of its sides.

Uses
The Big Wheel on the popular US game show The Price Is Right has an icosagonal cross-section.

The Globe, the outdoor theater used by William Shakespeare's acting company, was discovered to have been built on an icosagonal foundation when a partial excavation was done in 1989.Muriel Pritchett, University of Georgia "To Span the Globe" , see also Editor's Note, retrieved on 10th January 2016

As a golygonal path, the swastika is considered to be an irregular icosagon.

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A regular square, pentagon, and icosagon can completely fill a plane vertex.

 Dissection
Coxeter states that every parallel-sided 2m-gon can be divided into m(m-1)/2 rhombs. For the icosagon, m=10, and it can be divided into 45: 5 squares and 4 sets of 10 rhombs. This decomposition is based on a Petrie polygon projection of a 10-cube, with 45 of 11520 faces. Coxeter, Mathematical recreations and Essays, Thirteenth edition, p.141 The list A006245 enumerates the number of solutions as 18,410,581,880, including up to 20-fold rotations and chiral forms in reflection.
+ Dissection into 45 rhombs160px160px

References

Naming Polygons and Polyhedra 
icosagon

20