enneadecagon

In geometry, an enneadecagon is a polygon with 19 sides and angles.

A regular enneadecagon cannot be constructed using a compass and straightedge.

The regular enneadecagon is the Petrie polygon for one higher dimensional polytope, projected in a skew orthogonal projection:

When only an angle trisector is permitted, there is a complete description of all regular polygons which can be constructed, including above mentioned regular heptagon, triskaidecagon (13-gon) and enneadecagon (19-gon).