Enneadecagon

An enneadecagon or 19-gon is a shape with 19 sides and 19 corners.^[1] It is also known as an enneakaidecagon or a nonadecagon.^[2]

Regular enneadecagon
A regular enneadecagon
Type	Regular polygon
Edges and vertices	19
Schläfli symbol	{19}
Coxeter diagram
Symmetry group	Dihedral (D19), order 2×19
Internal angle (degrees)	≈161.052°
Dual polygon	Self
Properties	Convex, cyclic, equilateral, isogonal, isotoxal

Regular enneadecagon

All sides of a regular enneadecagon are the same length. Each corner is ≈161.052°. All corners added together equal 3060°.

The radius of the circumcircle of the regular enneadecagon with side length t is ${\displaystyle R={\frac {t}{2}}\csc {\frac {180}{19}}}$ (angle in degrees). The area, where t is the edge length, is ${\displaystyle {\frac {19}{4}}t^{2}\cot {\frac {\pi }{19}}\simeq 28.4652\,t^{2}.}$