Nonagon (Concave)
When I began my website pages, I first dealt with polygons of 3, 6, 8 and 12 sides. I did my constructions with those and then returned to a nonagon -- 9-sided. Also named an Enneagon. The nonagon is not constructable in the classic sense with straight edge and compass. However, there are methods to approximate the nonagon fairly closely. I attempted one of the methods to produce my example below. (My media directory contains three images of accurate nonagons which I must have picked out of Wikipedia. They are named Cheater and Cheater5 and Moslion.)
There might be excursions into 5-sided, 7-sided, and 10-sided. I don't believe I have seen any examples of those types. I vaguely remember something about a 20-sided object, but that might have been a solid - icosahedron. Ah, yes, solids. It might be interesting to explore drawing of 3-D solids. In the '60s, I believe some of Everett Van Akin's acrylic paintings were pictures of solids.
But here is the nonagon created via some construction method. I was just interested in its construction and then moved on to Reuleaux work. I did not take much time with it as can be seen in the fact that the interior polygon is not at all regular as it should be. My choice of colors might be improved also. (Bingo)