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Blue Sierpinski carpet, 6th step of a plane fractal. Square, cut into a 3-by-3 grid, the central subsquare is then removed. Same procedure applied recursively to remaining 8 sub squares, ad infinitum.
Sierpinski triangle, a plane fractal, seventh iteration step. Starting with a triangle, subdivided into four smaller triangles, removing the central one. Repeating step two with each smaller triangle.