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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
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified January 27 22:40 EST 2022. Contains 350654 sequences. (Running on oeis4.)