A cellular automaton that yields a pattern whose shape closely approximates a circle. The rule used is of the same kind as on the previous page, but now takes the center cell to become black only if it has exactly 3 black neighbors. If it has 1, 2 or 4 black neighbors then it stays the same color as it was before, and if it has 5 or more black neighbors, then it becomes white on the next step (code number 746). The initial condition consists of a row of 7 black cells, just as in the picture on the previous page. The pattern shown here is the result of 400 steps in the evolution of the system. After t steps, the radius of the approximate circle is about 0.37t.

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