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A267209
Binary representation of the middle column of the "Rule 109" elementary cellular automaton starting with a single ON (black) cell.
1
1, 11, 111, 1110, 11101, 111011, 1110110, 11101101, 111011011, 1110110110, 11101101101, 111011011011, 1110110110110, 11101101101101, 111011011011011, 1110110110110110, 11101101101101101, 111011011011011011, 1110110110110110110, 11101101101101101101
OFFSET
0,2
REFERENCES
S. Wolfram, A New Kind of Science, Wolfram Media, 2002; p. 55.
FORMULA
Conjectures from Colin Barker, Jan 13 2016 and Apr 19 2019: (Start)
a(n) = 10*a(n-1)+a(n-3)-10*a(n-4) for n>3.
G.f.: (1+x+x^2-x^3) / ((1-x)*(1-10*x)*(1+x+x^2)).
(End)
MATHEMATICA
rule=109; 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 *) mc=Table[catri[[k]][[k]], {k, 1, rows}]; (* Keep only middle cell from each row *) Table[FromDigits[Take[mc, k]], {k, 1, rows}] (* Binary Representation of Middle Column *)
CROSSREFS
Cf. A243566.
Sequence in context: A266624 A266790 A266592 * A110444 A265380 A114397
KEYWORD
nonn,easy
AUTHOR
Robert Price, Jan 11 2016
STATUS
approved