OpenSCAD code for a Sierpinski tetrahedron. Parameters for thickness, size, depth of recursion. I learned a couple of things from an earlier version. One is, if recursion is involved, do the recursion in the OpenSCAD language (not Python) to allow OpenSCAD to perform optimizations that vastly reduce the run time. Where there are lots of intersections of objects with a $fn parameter, the run time is more than quadratic in $fn, so the cost of smooth curves is high.