A211292 a(n) = number of n-lettered words in the alphabet {1, 2, 3} with as many occurrences of the substring (consecutive subword) [1, 1, 2] as of [2, 1, 1].

1, 3, 9, 25, 71, 205, 591, 1707, 4941, 14319, 41541, 120643, 350713, 1020483, 2972017, 8663153, 25273679, 73793509, 215632759, 630591329, 1845473587, 5404857441, 15840441819, 46456569717, 136337104383, 400367192229, 1176443166855, 3458933456085, 10175673610119, 29951939863389

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: A211301 A211295 A211289 * A291683 A079857 A265940

Adjacent sequences: A211289 A211290 A211291 * A211293 A211294 A211295

Keyword

nonn

Author

N. J. A. Sloane, Apr 07 2012

Status

approved