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%I #17 Aug 15 2015 16:52:54
%S 0,4,38,328,2686,21224,163982,1249784,9447102,71056840,532854638,
%T 3988597144,29822927134,222836912744,1664351910350,12427793513528,
%U 92784673372542,692656225953544,5170521713987630,38595421782328024,288089831076277726,2150375933904641960
%N Number of forests in Moebius ladder M_n.
%H Colin Barker, <a href="/A020865/b020865.txt">Table of n, a(n) for n = 0..1000</a>
%H J. P. McSorley, <a href="http://dx.doi.org/10.1016/S0012-365X(97)00086-1">Counting structures in the Moebius ladder</a>, Discrete Math., 184 (1998), 137-164.
%H <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (16,-87,200,-208,96,-16).
%F a(n) = (4+sqrt(12))^n+(4-sqrt(12))^n+2^n-(5/2+1/2*sqrt(17))^n-(5/2-1/2*sqrt(17))^n-1.
%F G.f.: 2*x*(2-13*x+34*x^2-28*x^3+8*x^4) / ( (x-1)*(2*x-1)*(4*x^2-8*x+1)*(2*x^2-5*x+1) ).
%o (PARI) concat(0, Vec(2*x*(8*x^4-28*x^3+34*x^2-13*x+2)/((x-1)*(2*x-1)*(2*x^2-5*x+1)*(4*x^2-8*x+1)) + O(x^30))) \\ _Colin Barker_, Aug 02 2015
%K nonn,easy
%O 0,2
%A _N. J. A. Sloane_
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