%I
%S 1,4,14,50,182,668,2466,9156,34186,128308,483880,1832836,6970186,
%T 26603704,101875408,391282036,1506881410,5817328360,22507181024,
%U 87252861140,338857359792,1318133110848,5135008140588,20031069560880,78234143417074,305894382472336,1197260125948652,4690409375327972
%N a(n) = number of nlettered words in the alphabet {1, 2, 3, 4} with as many occurrences of the substring (consecutive subword) [1, 2] as of [2, 3].
%H Alois P. Heinz, <a href="/A211308/b211308.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 08 2012
