
An extended Menger Sponge -iteration 2- displaying the 378 first digits -base 2- of 'pi' [Une éponge de Menger généralisée -itération 2- visualisant les 378 premiers chiffres -base 2- de 'pi'].
                     log(20)
                    --------- = 2.726833027860842...
                     log(3)
The "standard" Menger sponge can be defined by means of subdivision rules.
Here is the way how each of the 27 cubes of the "standard" Menger sponge at a given level is subdivided:
                    
                   "standard"  Menger sponge
                     _____________________
                    /                     \
 
                    TTT       TFT       TTT
                    TFT       FFF       TFT
                    TTT       TFT       TTT
 
                    \_/
 
             Sierpinski carpet
or again:
TTT TFT TTT TFT FFF TFT TTT TFT TTTwhere 'T' ('True') and 'F' ('False') means respectively "subdivide the current cube" and "do not subdivide and destroy the current cube". The rules are repeated at each level, but they can be changed periodically and for example:
                    
                    TTT TFT TTT  TFT FFF TFT  TTT TFT TTT   FFF FTF FFF  FTF TTT FTF  FFF FTF FFF
 
                    \___________________________________/   \___________________________________/
 
                          "standard"  Menger sponge                      complement
alternates the "standard" Menger sponge and its complement.
Obviously many other rules do exist as shown below...
                    0 --> F
                    1 --> T