The 3D Sierpinski Gasket (Tetrix) is formed by starting with a solid regular tetrahedron, scaling it by a factor of
r = 1/2, and placing 4 identical copies at the 4 vertices of the original.
The 3D Menger Sponge divides a cube into 27 sub-cubes ($3 \times 3 \times 3$) and removes the 6 center face cubes and 1 central core cube, leaving $N = 20$ cubes of size $r = 1/3$.