A211297 a(n) = number of n-lettered words in the alphabet {1, 2, 3} with as many occurrences of the substring (consecutive subword) [1, 2, 1] as of [1, 3, 1].

1, 3, 9, 25, 69, 195, 555, 1573, 4457, 12677, 36165, 103323, 295639, 847587, 2434755, 7006089, 20193261, 58296927, 168567687, 488155597, 1415686337, 4111268669, 11955274925, 34808988199, 101471734355, 296139036809, 865204909777, 2530413173787, 7407817001559, 21706686476055, 63662015359655

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: A211293 A211291 A211294 * A370227 A297590 A244934

Adjacent sequences: A211294 A211295 A211296 * A211298 A211299 A211300

Keyword

nonn

Author

N. J. A. Sloane, Apr 07 2012

Status

approved