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A305694 Number of length-n binary words containing no instance of the pattern x y y x^R where x and y are nonempty. 0
1, 2, 4, 8, 12, 18, 22, 28, 38, 50, 56, 68, 84, 102, 118, 142, 172, 204, 228, 264, 308, 358, 412, 478, 558, 654, 764, 892, 1048, 1234, 1404, 1618, 1870, 2152, 2458, 2826, 3256, 3750, 4292, 4940, 5688, 6548, 7518, 8672, 10004, 11520, 13184, 15130, 17364, 19904 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

By an "instance of the pattern x y y x^R" we mean a nonempty block, followed by a second nonempty block (of a possibly different length), followed by the second block again, and ending with the first block reversed. An example in English is the word "redder": (re)(d)(d)(er).

LINKS

Table of n, a(n) for n=0..49.

CROSSREFS

Sequence in context: A046843 A292060 A152125 * A176562 A100057 A007590

Adjacent sequences:  A305691 A305692 A305693 * A305695 A305696 A305697

KEYWORD

nonn

AUTHOR

Jeffrey Shallit, Jun 08 2018

STATUS

approved

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Last modified August 20 04:52 EDT 2019. Contains 326139 sequences. (Running on oeis4.)