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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
OFFSET
0,2
LINKS
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: A047065 A047008 A055990 * A087945 A051924 A272687
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Apr 08 2012
STATUS
approved