21-8 step prism

The 21-8 step prism is a convex isogonal polychoron, member of the step prism family. It has 84 phyllic disphenoids of two kinds as cells.

The ratio between the longest and shortest edges is 1:$\sqrt{(11cos(2π/7)-1)/(12cos(2π/7)-5)}$ ≈ 1:1.53638.

Vertex coordinates
Coordinates for the vertices of a 21-8 step prism of circumradius $\sqrt{2}$ are given by: where k is an integer from 0 to 20.
 * (sin(2πk/21), cos(2πk/21), sin(16πk/21), cos(15πk/21)),