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A211308 a(n) = number of n-lettered words in the alphabet {1, 2, 3, 4} with as many occurrences of the substring (consecutive subword) [1, 2] as of [2, 3]. 1
1, 4, 14, 50, 182, 668, 2466, 9156, 34186, 128308, 483880, 1832836, 6970186, 26603704, 101875408, 391282036, 1506881410, 5817328360, 22507181024, 87252861140, 338857359792, 1318133110848, 5135008140588, 20031069560880, 78234143417074, 305894382472336, 1197260125948652, 4690409375327972 (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: A047008 A047065 A055990 * A087945 A051924 A272687

Adjacent sequences:  A211305 A211306 A211307 * A211309 A211310 A211311

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Apr 08 2012

STATUS

approved

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Last modified December 13 12:49 EST 2018. Contains 318086 sequences. (Running on oeis4.)