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%I M3575 #36 Dec 28 2017 18:52:56
%S 1,4,21,127,831,5722,40879,300440,2258455,17291704,134417955,
%T 1058279251,8422155293,67647554826,547699155261,4465275681735,
%U 36627214297455,302067234113560,2503174651819435,20832888975309257,174057811108059017,1459365504991034106
%N Number of Havender tableaux of height 2 with n columns.
%D D. Gouyou-Beauchamps, "Tableaux de Havender standards," in S. Brlek, editor, Parallélisme: Modèles et Complexité. LACIM, Université du Québec à Montréal, 1989.
%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H Alois P. Heinz, <a href="/A007345/b007345.txt">Table of n, a(n) for n = 0..1000</a>
%H D. Gouyou-Beauchamps, <a href="/A007345/a007345.pdf">Tableaux de Havender standards</a>, Parallélisme: Modèles et Complexité. LACIM, Université du Québec à Montréal, 1989. (Annotated scanned copy)
%F G.f.: (sqrt(1-5*x^2) - sqrt(1-9*x^2)) / (2 * x^2 * sqrt(1-x^2)) [from Gouyou-Beauchamps]. - _Sean A. Irvine_, Dec 28 2017
%F a(n) = Sum_{q=0..2*n} Sum_{j=max(0, n-q)..floor((2*n-q)/2)} n! * (4*n-2*q-2*j)! / ((2*n-q-2*j)! * (j+1)! * ((2*n-q-j)!)^2 * (q-n+j)!) [from Gouyou-Beauchamps]. - _Sean A. Irvine_, Dec 28 2017
%Y Row sums of A259992.
%K nonn
%O 0,2
%A _N. J. A. Sloane_, _Mira Bernstein_
%E More terms from _Sean A. Irvine_, Dec 28 2017
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