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%I #12 Sep 10 2020 20:12:53
%S 1,3,9,25,71,205,591,1707,4941,14319,41541,120643,350713,1020483,
%T 2972017,8663153,25273679,73793509,215632759,630591329,1845473587,
%U 5404857441,15840441819,46456569717,136337104383,400367192229,1176443166855,3458933456085,10175673610119,29951939863389
%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, 1].
%H Alois P. Heinz, <a href="/A211292/b211292.txt">Table of n, a(n) for n = 0..1000</a>
%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
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