A211294 a(n) = number of n-lettered words in the alphabet {1, 2, 3} with as many occurrences of the substring (consecutive subword) [1, 1, 2] as of [2, 2, 1].

1, 3, 9, 25, 69, 193, 543, 1533, 4341, 12331, 35131, 100369, 287511, 825643, 2376563, 6855891, 19818729, 57402023, 166556929, 484093953, 1409218111, 4108293369, 11993207211, 35055708423, 102587243163, 300540887595, 881366127909, 2587147501819, 7600984533115, 22349936569297, 65768286284401

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: A211300 A211293 A211291 * A211297 A370227 A297590

Adjacent sequences: A211291 A211292 A211293 * A211295 A211296 A211297

Keyword

nonn

Author

N. J. A. Sloane, Apr 07 2012

Status

approved