A211281 a(n) = number of n-lettered words in the alphabet {1, 2, 3} with as many occurrences of the substring (consecutive subword) [1, 2] as of [2, 3].

1, 3, 7, 17, 45, 123, 337, 927, 2575, 7225, 20427, 58085, 165967, 476241, 1371615, 3962817, 11480157, 33335691, 96998137, 282751095, 825549445, 2413818011, 7066833237, 20713316043, 60775993945, 178497281223, 524702227369, 1543636437591, 4544652411561, 13389233104135, 39471952247297

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: A087953 A210839 A261235 * A233656 A106191 A062810

Adjacent sequences: A211278 A211279 A211280 * A211282 A211283 A211284

Keyword

nonn

Author

N. J. A. Sloane, Apr 07 2012

Status

approved