A211293 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, 1, 3].

1, 3, 9, 25, 69, 191, 531, 1485, 4173, 11779, 33381, 94947, 270979, 775809, 2227607, 6413441, 18510645, 53548119, 155231177, 450869943, 1311874981, 3823307463, 11159216577, 32615423715, 95446283091, 279639107073, 820162536291, 2407847745541, 7075424461287, 20808497810757, 61244466778891

Offset

0,2

Links

Table of n, a(n) for n=0..30.

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: A211296 A098182 A211300 * A211291 A211294 A211297

Adjacent sequences: A211290 A211291 A211292 * A211294 A211295 A211296

Keyword

nonn

Author

N. J. A. Sloane, Apr 07 2012

Status

approved