Press 'S' to draw the next iteration. 1x'S' = 4 pyramids, 16 triangles. 2x'S' = 16 pyramids, 64 triangles. 3x'S' = 64 pyramids, 256 triangles. 4x'S' = 256 pyramids, 1024 triangles. ... Mouse to rotate.
Added filler-request by @raucket How many times can you press S? My computer can only make it to 4 before the program is so slow that the entire tetrahedron cannot be filled in one frame (the whole thing is rendered so slowly that for a little bit it only shows you part of it.