A211287 a(n) = number of n-lettered words in the alphabet {1, 2, 3} with as many occurrences of the substring (consecutive subword) [1, 1, 1] as of [2, 2, 2].

1, 3, 9, 25, 71, 201, 571, 1621, 4611, 13127, 37415, 106763, 304991, 872267, 2497519, 7159191, 20545393, 59028011, 169782251, 488892391, 1409342969, 4067217153, 11750311255, 33983345183, 98387605609, 285144063989, 827236307471, 2402300281607, 6983098390213, 20318073613437, 59172567046657

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: A101197 A233828 A101168 * A211290 A211299 A211301

Adjacent sequences: A211284 A211285 A211286 * A211288 A211289 A211290

Keyword

nonn

Author

N. J. A. Sloane, Apr 07 2012

Status

approved