Menger sponge

A Menger sponge is a square which is similar to itself. To make a Menger sponge, take a square, and cut a square hole in the middle. Repeat the process around the edge of the square 9 times. Do the same thing aforementioned infinitely.

Menger Sponge Media

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  An illustration of M4, the sponge after four iterations of the construction process

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  An illustration of the iterative construction of a Menger sponge up to M3, the third iteration

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  the red figure was the figure before this figure.

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  Sierpinski–Menger snowflake