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, 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

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: A047065 A047008 A055990 * A087945 A051924 A272687

Adjacent sequences: A211305 A211306 A211307 * A211309 A211310 A211311

Keyword

nonn

Author

N. J. A. Sloane, Apr 08 2012

Status

approved