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A260450 Infinite palindromic word (a(1),a(2),a(3),...) with initial word w(1) = (1,3,2) and midword sequence (a(n)); see Comments. 2
1, 3, 2, 1, 2, 3, 1, 3, 1, 3, 2, 1, 2, 3, 1, 2, 1, 3, 2, 1, 2, 3, 1, 3, 1, 3, 2, 1, 2, 3, 1, 1, 1, 3, 2, 1, 2, 3, 1, 3, 1, 3, 2, 1, 2, 3, 1, 2, 1, 3, 2, 1, 2, 3, 1, 3, 1, 3, 2, 1, 2, 3, 1, 2, 1, 3, 2, 1, 2, 3, 1, 3, 1, 3, 2, 1, 2, 3, 1, 2, 1, 3, 2, 1, 2, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

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

EXAMPLE

w(1) = 132, the initial word.

w(2) = 1321231 ( = 132+1+231, where + = concatenation)

w(3) = w(2)+2+w(2)*

w(4) = w(3)+3+w(3)*

MATHEMATICA

u[1] = {1, 3, 2}; 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]]}; v = u[8]

CROSSREFS

Cf. A260390, A260449.

Sequence in context: A068929 A060567 A174543 * A036583 A047878 A256427

Adjacent sequences:  A260447 A260448 A260449 * A260451 A260452 A260453

KEYWORD

nonn,easy

AUTHOR

Clark Kimberling, Aug 24 2015

STATUS

approved

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Last modified May 24 06:53 EDT 2019. Contains 323529 sequences. (Running on oeis4.)