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A169648
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Number of cells that are turned from OFF to ON at stage n in Wolfram's 2-D cellular automaton defined by Rule 942.
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10
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0, 1, 4, 4, 12, 8, 12, 12, 36, 28, 12, 12, 36, 28, 36, 36, 108, 100, 12, 12, 36, 28, 36, 36, 108, 92, 36, 36, 108, 84, 108, 108, 324, 340, 12, 12, 36, 28, 36, 36, 108, 92, 36, 36, 108, 84, 108, 108, 324, 316, 36, 36, 108, 84, 108, 108, 324, 276, 108, 108, 324
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OFFSET
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-1,3
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COMMENTS
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We work on the square grid. A cell is turned ON iff exactly one or four of its four neighbors is ON. Once a cell is ON it stays ON. At stage -1 all cells are OFF. At stage 0 a single cell is turned ON.
This sequence also arises from Rule 467 (New Kind of Science, page 173) if we count white cells, black cells in alternate generations. - N. J. A. Sloane, Feb 04 2015
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REFERENCES
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S. Wolfram, A New Kind of Science, Wolfram Media, 2002; p. 928.
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LINKS
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FORMULA
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Added Apr 15 2010: The sequence is the sum of A147582(n) and 4 times A169689(4n), both of which have simple explicit formulas for the n-th term. See those two entries for details.
The sequence is generated by the following recurrence (this is true, but unnecessarily complicated): Take a(0),...,a(7) as initial values.
For n >= 8, write n = 2^k + j with 0 <= j < 2^k. Then:
a(2^k)=3a(2^(k-1))+3*2^(k-1)-8 (this is for j=0),
a(3*2^(k-1))=3a(3*2^(k-2))+2^(k+1)-24 (this is for j=2^(k-1)),
and otherwise
a(2^k+j)=a(2^(k-1)+j) for 0 < j < 2^(k-1)-1,
a(2^k+j)=3a(2^(k-1)+j) for 2^(k-1) < j < 2^k.
The leading terms in the rows are essentially 4*A169651, and the "midpoints" of the rows are essentially 4*A169650.
See A169688, A169689 for a simpler (but equivalent) recurrence for this sequence.
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EXAMPLE
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May be written as a triangle:
0,
1,
4,12,
8,12,12,36,
28,12,12,36,28,36,36,108,
100,12,12,36,28,36,36,108,92,36,36,108,84,108,108,324,
340,12,12,36,28,36,36,108,92,36,36,108,84,108,108,324,316,36,...
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CROSSREFS
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KEYWORD
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nonn,tabf
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AUTHOR
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STATUS
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approved
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