This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A160873 #27 Sep 08 2022 08:45:45
%S A160873 0,3,42,420,3720,31248,256032,2072640,16679040,133824768,1072169472,
%T A160873 8583644160,68694312960,549655154688,4397643866112,35182761492480,
%U A160873 281468534292480,2251774043947008,18014295430397952,144114775759257600
%N A160873 Number of isomorphism classes of connected (D_4)-fold coverings of a connected graph with circuit rank n.
%C A160873 Previous name: "Regular coverings having dihedral voltage groups: see Kwak-Lee reference in A160870 for precise definition."
%C A160873 From _Álvar Ibeas_, Oct 30 2015: (Start)
%C A160873 Also, number of isomorphism classes of connected (C_4 x C_2)-fold coverings of a connected graph with circuit rank n.
%C A160873 Also, number of lattices L in Z^n such that the quotient group Z^n / L is C_4 x C_2.
%C A160873 Also, number of subgroups of (C_4)^n isomorphic to C_4 x C_2.
%C A160873 (End)
%D A160873 J. H. Kwak and J. Lee, Enumeration of graph coverings, surface branched coverings and related group theory, in Combinatorial and Computational Mathematics (Pohang, 2000), ed. S. Hong et al., World Scientific, Singapore 2001, pp. 97-161.
%H A160873 Álvar Ibeas, <a href="/A160873/b160873.txt">Table of n, a(n) for n = 1..1000</a>
%H A160873 J. H. Kwak, J.-H. Chun, and J. Lee, <a href="http://dx.doi.org/10.1137/S0895480196304428">Enumeration of regular graph coverings having finite abelian covering transformation groups</a>, SIAM J. Discrete Math. 11(2), 1998, pp. 273-285.
%H A160873 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (14,-56,64).
%F A160873 a(n) = 2^(n-2) * (2^n - 1) * (2^(n-1) - 1) = 8^(n-1) - 6*4^(n-2) + 2^(n-2) [Kwak, Chun, and Lee]. - _Álvar Ibeas_, Oct 30 2015
%F A160873 From _Colin Barker_, Oct 30 2015: (Start)
%F A160873 a(n) = 2^(-3+n) * (2-3*2^n+4^n).
%F A160873 a(n) = 14*a(n-1)-56*a(n-2)+64*a(n-3) for n>3.
%F A160873 G.f.: -3*x^2/((2*x-1)*(4*x-1)*(8*x-1)). (End)
%t A160873 Table[2^(-3+n)*(2-3*2^n+4^n), {n,1,30}] (* or *) LinearRecurrence[{14, -56, 64}, {0, 3, 42}, 30] (* _G. C. Greubel_, Apr 30 2018 *)
%o A160873 (PARI) a(n) = 2^(-3+n) * (2-3*2^n+4^n) \\ _Colin Barker_, Oct 30 2015
%o A160873 (PARI) concat(0, Vec(-3*x^2/((2*x-1)*(4*x-1)*(8*x-1)) + O(x^30))) \\ _Colin Barker_, Oct 30 2015
%o A160873 (Magma) [2^(-3+n)*(2-3*2^n+4^n): n in [1..30]]; // _G. C. Greubel_, Apr 30 2018
%K A160873 nonn,easy
%O A160873 1,2
%A A160873 _N. J. A. Sloane_, Nov 15 2009
%E A160873 Name clarified by _Álvar Ibeas_, Oct 30 2015