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%I #10 Mar 03 2017 19:40:53
%S 1,3,9,25,69,191,531,1485,4173,11779,33381,94947,270979,775809,
%T 2227607,6413441,18510645,53548119,155231177,450869943,1311874981,
%U 3823307463,11159216577,32615423715,95446283091,279639107073,820162536291,2407847745541,7075424461287,20808497810757,61244466778891
%N 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].
%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