A211277 a(n) = number of n-lettered words in the alphabet {1, 2, 3} with as many occurrences of the substring (consecutive subword) [1, 1] as of [2, 2].

1, 3, 7, 17, 43, 109, 285, 753, 2029, 5529, 15265, 42531, 119557, 338357, 963447, 2756727, 7921673, 22843917, 66078463, 191637251, 557045705, 1622405135, 4733543307, 13831907295, 40473954863, 118578027369, 347789276215, 1021094753633, 3000649670809, 8825309734939, 25976499888045

Offset

0,2

Links

Alois P. Heinz, Table of n, a(n) for n = 0..1000

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: A161943 A134184 A142975 * A114589 A192908 A078679

Adjacent sequences: A211274 A211275 A211276 * A211278 A211279 A211280

Keyword

nonn

Author

N. J. A. Sloane, Apr 07 2012

Status

approved