A261204 Number of binary strings of length n that avoid the pattern x x^R x (x^R is the reversal of x).

1, 2, 4, 6, 10, 16, 24, 34, 50, 72, 100, 138, 188, 254, 342, 454, 598, 784, 1018, 1316, 1694, 2166, 2756, 3492, 4404, 5530, 6920, 8626, 10712, 13264, 16368, 20134, 24700, 30212, 36856, 44850, 54438, 65918, 79642, 96008, 115488, 138642, 166100, 198614, 237062

Offset

0,2

Links

Giovanni Resta, Table of n, a(n) for n = 0..100

James D. Currie, Narad Rampersad, Binary words avoiding x x^R x and strongly unimodal sequences, arXiv:1508.02964 [math.CO], 2015.

James D. Currie, Narad Rampersad, Binary words avoiding x x^R x and strongly unimodal sequences, Journal of Integer Sequences, Vol. 18 (2015), Article 15.10.3.

Example

For n = 6, the substrings to be avoided are 000, 111, 011001, and 100110. There are 26 binary strings that avoid 000 and 111, so there are 26 - 2 = 24 binary strings of length 6 that avoid x x^R x.

Crossrefs

Cf. A028445, A241903.

Sequence in context: A327047 A332281 A241903 * A293422 A132002 A098151

Adjacent sequences: A261201 A261202 A261203 * A261205 A261206 A261207

Keyword

nonn

Author

Narad Rampersad, Aug 11 2015

Extensions

a(25)-a(44) from Giovanni Resta, Aug 12 2015

Status

approved