18-2 step prism

The 18-2 step prism is a convex isogonal polychoron and a member of the step prism family. It has 9 rhombic disphenoids and 126 phyllic disphenoids of six kinds as cells, with 30 (2 rhombic and 28 phyllic disphenoids) joining at each vertex.

Vertex coordinates
Coordinates for the vertices of a 18-2 step prism inscribed in an octadecagonal duoprism with base lengths a and b are given by: where k is an integer from 0 to 17. If the edge length differences are to be minimized, the ratio of a:b must be equivalent to 1:$$1+2\cos\frac\pi9$$ ≈ 1:2.87939.
 * (a*sin(πk/9), a*cos(πk/9), b*sin(2πk/9), b*cos(2πk/9)),