A211289 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 [1, 2, 1].

1, 3, 9, 25, 71, 204, 582, 1664, 4774, 13705, 39395, 113437, 327077, 944320, 2730140, 7903408, 22907996, 66480105, 193156593, 561852041, 1636108387, 4769383420, 13917292514, 40651107056, 118849691074, 347788333857, 1018607452047, 2985778561717, 8758943057489, 25714264110112, 75545780021240

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: A211299 A211301 A211295 * A211292 A291683 A079857

Adjacent sequences: A211286 A211287 A211288 * A211290 A211291 A211292

Keyword

nonn

Author

N. J. A. Sloane, Apr 07 2012

Status

approved