Grand tridecagram

The grand tridecagram, or gat, is a non-convex polygon with 13 sides. It's created by taking the fifth stellation]] of a tridecagon. A regular grand tridecagram has equal sides and equal angles.

It is one of five regular 13-sided star polygons, the other four being the small tridecagram, the tridecagram, the medial tridecagram, and the great tridecagram.