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

A 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]

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 ${\displaystyle {\frac {19}{4}}t^{2}\cot {\frac {\pi }{19}}\simeq 28.4652\,t^{2}.}$