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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].
0
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
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
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Apr 07 2012
STATUS
approved