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A079316
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Number of first-quadrant cells (including the two boundaries) that are ON at stage n of the cellular automaton described in A079317.
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6
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1, 3, 3, 7, 5, 11, 9, 21, 11, 25, 15, 35, 19, 45, 29, 73, 31, 77, 35, 87, 39, 97, 49, 125, 53, 135, 63, 163, 73, 191, 101, 273, 103, 277, 107, 287, 111, 297, 121, 325, 125, 335, 135, 363, 145, 391, 173, 473, 177, 483, 187, 511, 197, 539, 225, 621, 235, 649, 263, 731
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OFFSET
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0,2
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COMMENTS
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Start with cell (0,0) active; at each succeeding stage the cells that share exactly one edge with an active cell change their state.
The pattern has 4-fold symmetry; sequence just counts cells in one quadrant.
This is not the CA discussed by Singmaster in the reference given in A079314. That was an error based on my misreading of the paper. - N. J. A. Sloane, Aug 05 2009
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REFERENCES
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D. Singmaster, On the cellular automaton of Ulam and Warburton, M500 Magazine of the Open University, #195 (December 2003), pp. 2-7.
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LINKS
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PROG
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(PARI) M=matrix(101, 101); M[1, 1]=1; for(s=1, 100, c=[]; a=M[1, 1]; for(x=2, 100, for(y=2, 100, a+=M[x, y]; if(M[x-1, y]+M[x+1, y]+M[x, y-1]+M[x, y+1]==1, c=concat(c, [[x, y]]) )); a+=M[x, 1]+M[1, x]; if(M[x, 2]==0 && M[x-1, 1]+M[x+1, 1]==1, c=concat(c, [[x, 1]]) ); if(M[2, x]==0 && M[1, x-1]+M[1, x+1]==1, c=concat(c, [[1, x]]) )); print1(a, ", "); for(i=1, length(c), M[c[i][1], c[i][2]]=1-M[c[i][1], c[i][2]]) ) - Max Alekseyev, Feb 02 2007
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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