A211304 a(n) = number of n-lettered words in the alphabet {1, 2, 3, 4} with as many occurrences of the substring (consecutive subword) [1, 1] as of [2, 2].

1, 4, 14, 50, 180, 650, 2364, 8640, 31760, 117350, 435828, 1626440, 6097584, 22958876, 86796152, 329371312, 1254263360, 4791746342, 18360757572, 70546266792, 271734956048, 1049090621300, 4058741094088, 15732659133968, 61090481362816, 237596524586044, 925427051663624, 3609324005099408

Offset

0,2

Links

Table of n, a(n) for n=0..27.

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: A055099 A335921 A153367 * A047065 A047008 A055990

Adjacent sequences: A211301 A211302 A211303 * A211305 A211306 A211307

Keyword

nonn

Author

N. J. A. Sloane, Apr 08 2012

Status

approved