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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

Index entries for sequences related to cellular automata

Index to Elementary Cellular Automata

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.)