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 A266327 Binary representation of the n-th iteration of the "Rule 20" elementary cellular automaton starting with a single ON (black) cell. 1
 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Rules 52, 148 and 180 also generate this sequence. REFERENCES S. Wolfram, A New Kind of Science, Wolfram Media, 2002; p. 55. LINKS Robert Price, Table of n, a(n) for n = 0..1000 Eric Weisstein's World of Mathematics, Elementary Cellular Automaton S. Wolfram, A New Kind of Science FORMULA Conjectures from Colin Barker, Dec 28 2015 and Apr 18 2019: (Start) a(n) = 6-5*(-1)^n. a(n) = a(n-2) for n>1. G.f.: (1+11*x) / ((1-x)*(1+x)). (End) MATHEMATICA rule=20; rows=20; ca=CellularAutomaton[rule, {{1}, 0}, rows-1, {All, All}]; (* Start with single black cell *) catri=Table[Take[ca[[k]], {rows-k+1, rows+k-1}], {k, 1, rows}]; (* Truncated list of each row *) Table[FromDigits[catri[[k]]], {k, 1, rows}] (* Binary Representation of Rows *) CROSSREFS Cf. A266326. Sequence in context: A231920 A230891 A063431 * A274216 A280524 A317845 Adjacent sequences:  A266324 A266325 A266326 * A266328 A266329 A266330 KEYWORD nonn,easy AUTHOR Robert Price, Dec 27 2015 STATUS approved

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Last modified July 19 12:49 EDT 2019. Contains 325159 sequences. (Running on oeis4.)