A305694 Number of length-n binary words containing no instance of the pattern x y y x^R where x and y are nonempty.

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

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: A292060 A152125 A338097 * A176562 A337120 A100057

Adjacent sequences: A305691 A305692 A305693 * A305695 A305696 A305697

Keyword

nonn

Author

Jeffrey Shallit, Jun 08 2018

Status

approved