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A260397 Infinite palindromic word (a(1),a(2),a(3),...) with initial word w(1) = (1,1,0) and midword sequence (a(n)); see Comments. 6
1, 1, 0, 1, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 1, 0, 1, 1, 0, 1, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 1, 0, 1, 1, 0, 1, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 1, 0, 1, 1, 0, 1, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 1, 0, 1, 1, 0, 1, 0, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

1

COMMENTS

Below, w* denotes the reversal of a word w, and "sequence" and "word" are interchangable. An infinite word is palindromic if it has infinitely many initial subwords w such that w = w*.

Many infinite palindromic words (a(1),a(2),...) are determined by an initial word w and a midword sequence (m(1),m(2),...) of palindromes, as follows: for given w of length k, take w(1) = w = (a(1),a(2),...,a(k)). Form the palindrome w(2) = w(1)m(1)w(1)* by concatenating w(1), m(1), and w(1)*. Continue inductively; i.e., w(n+1) = w(n)m(n)w(n)* for all n >= 1. See A260390 for examples.

LINKS

Clark Kimberling, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = 1 - A260445(n).

EXAMPLE

w(1) = 110, the initial word;

w(2) = w(1)+a(1)+w(1)* = 1101011 ( = 110+1+011, where + = concatenation);

w(3) = w(2)+a(2)+w(2)* = 110101111101011 (= 1101011+1+1101011);

w(4) = w(3)+a(3)+w(3)* = w(3)+0+w(3)*.

MATHEMATICA

u[1] = {1, 1, 0}; m[1] = {u[1][[1]]};

u[n_] := u[n] = Join[u[n - 1], m[n - 1], Reverse[u[n - 1]]];

m[k_] := {u[k][[k]]}; u[6]

CROSSREFS

Cf. A260390, A260445, A260394.

Sequence in context: A131372 A098457 A284793 * A137161 A077050 A128432

Adjacent sequences:  A260394 A260395 A260396 * A260398 A260399 A260400

KEYWORD

nonn,easy

AUTHOR

Clark Kimberling, Aug 13 2015

STATUS

approved

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Last modified November 22 08:33 EST 2019. Contains 329389 sequences. (Running on oeis4.)