Octagram

The octagram, or og, is a non-convex polygon with 8 sides. It's created by stellating the octagon. A regular octagram has equal sides and equal angles.

This is the second stellation of the octagon, and the only one that is not a compound. The only other polygons with a single non-compound stellation are the pentagon, the decagon, and the dodecagon.

Vertex coordinates
Coordinates for an octagram of unit edge length, centered at the origin, are all permutations of
 * (±($\sqrt{2–√2}$–1)/2, ±1/2).

Representations
An octagram has the following Coxeter diagrams:


 * x8/3o (full symmetry)
 * x4/3x (BC2 symmetry)