A211281 - OEIS

%I #8 Mar 03 2017 19:47:04

%S 1,3,7,17,45,123,337,927,2575,7225,20427,58085,165967,476241,1371615,

%T 3962817,11480157,33335691,96998137,282751095,825549445,2413818011,

%U 7066833237,20713316043,60775993945,178497281223,524702227369,1543636437591,4544652411561,13389233104135,39471952247297

%N 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].

%H Shalosh B. Ekhad and Doron Zeilberger, <a href="http://arxiv.org/abs/1112.6207">Automatic Solution of Richard Stanley's Amer. Math. Monthly Problem #11610 and ANY Problem of That Type</a>, arXiv preprint arXiv:1112.6207, 2011. See subpages for rigorous derivations of g.f., recurrence, asymptotics for this sequence.

%K nonn

%O 0,2

%A _N. J. A. Sloane_, Apr 07 2012