A211299 a(n) = number of n-lettered words in the alphabet {1, 2, 3} with as many occurrences of the substring (consecutive subword) [1, 2, 1] as of [2, 1, 3].

1, 3, 9, 25, 71, 202, 576, 1643, 4694, 13434, 38512, 110577, 317977, 915753, 2641181, 7628464, 22063605, 63899510, 185302479, 538032124, 1564079757, 4552119931, 13263345605, 38686346248, 112955785122, 330131225222, 965769993745, 2827820620683, 8287119688355, 24305919832796, 71344558858211

Offset

0,2

Links

Table of n, a(n) for n=0..30.

Shalosh B. Ekhad and Doron Zeilberger, Automatic Solution of Richard Stanley's Amer. Math. Monthly Problem #11610 and ANY Problem of That Type, arXiv preprint arXiv:1112.6207, 2011. See subpages for rigorous derivations of g.f., recurrence, asymptotics for this sequence.

Crossrefs

Sequence in context: A101168 A211287 A211290 * A211301 A211295 A211289

Adjacent sequences: A211296 A211297 A211298 * A211300 A211301 A211302

Keyword

nonn

Author

N. J. A. Sloane, Apr 07 2012

Status

approved