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%I #12 Nov 20 2015 05:11:38
%S 3,24,54,260,726,3096,10086,39940,140454,537624,1956246,7379204,
%T 27246966,102144024,379501254,1418981380,5285770566,19742287896,
%U 73621286646,274848860420
%N Number of perfect matchings in the twisted graph (C_4 X C_n)_{(13)(24)}.
%H Andrew Howroyd, <a href="/A220868/b220868.txt">Table of n, a(n) for n = 1..30</a>
%H S. Butler and S. Osborne, <a href="http://orion.math.iastate.edu/butler/papers/14_02_walks.pdf">Counting tilings by taking walks</a>, 2012.
%F Empirical g.f.: -x * (3*x^7 - 5*x^6 - 33*x^5 + 27*x^4 + 61*x^3 + 45*x^2 - 15*x - 3) / ( (x + 1) * (x^2 - 4*x + 1) * (x^2 - 2*x - 1) * (x^2 + 2*x - 1) ). - _Joerg Arndt_, Nov 17 2015
%K nonn
%O 1,1
%A _N. J. A. Sloane_, Dec 27 2012
%E a(1)-a(2),a(11)-a(20) from _Andrew Howroyd_, Nov 15 2015
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