Medial tridecagram

The medial tridecagram, or mat, is a non-convex polygon with 13 sides. It's created by taking the third stellation of a tridecagon. A regular medial 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 great tridecagram, and the grand tridecagram.