# Tridecagon

A tridecagon

A tridecagon or 13-gon is a shape with 13 sides and 13 corners.

## Regular tridecagon

All sides of a regular tridecagon are the same length. Each corner is 147.27°. All corners added together equal 6840°.

### Area

The amount of space a regular tridecagon takes up is

${\displaystyle A={\frac {13}{4}}a^{2}\cot {\frac {\pi }{13}}\simeq 13.1858\,a^{2}.}$

a is the length of one of its sides.

## Numismatic use

The regular tridecagon is used as the shape of the Czech 20 korun coin.[1]

## References

1. Colin R. Bruce, II, George Cuhaj, and Thomas Michael, 2007 Standard Catalog of World Coins, Krause Publications, 2006, Template:Isbn, p. 81.