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 A290470 #19 Feb 16 2025 08:33:49
%S A290470 3,7,15,59,143,367,1039,2755,7395,20007,53727,144635,389535,1048159,
%T A290470 2821535,7595267,20443523,55029319,148125295,398712379,1073232175,
%U A290470 2888862159,7776059055,20931132355,56341155043,151655701607,408217663167,1098815603707,2957725352255
%N A290470 Number of minimal edge covers in the n-Moebius ladder.
%H A290470 Andrew Howroyd, <a href="/A290470/b290470.txt">Table of n, a(n) for n = 1..200</a>
%H A290470 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/EdgeCover.html">Edge Cover</a>
%H A290470 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/MinimalEdgeCover.html">Minimal Edge Cover</a>
%H A290470 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/MoebiusLadder.html">Moebius Ladder</a>
%H A290470 <a href="/index/Rec#order_09">Index entries for linear recurrences with constant coefficients</a>, signature (1, 2, 6, 2, 2, -2, -2, -1, 1).
%F A290470 From _Andrew Howroyd_, Aug 04 2017: (Start)
%F A290470 a(n) = a(n-1) + 2*a(n-2) + 6*a(n-3) + 2*a(n-4) + 2*a(n-5) - 2*a(n-6) - 2*a(n-7) - a(n-8) + a(n-9) for n > 9.
%F A290470 G.f.: x*(1 + x)*(1 + 4*x^3 - 3*x^4)*(3 + x + x^2 - x^3)/((1 + x^2)*(1 + x + x^2 - x^3)*(1 - 2*x - 2*x^2 + x^4)).
%F A290470 (End)
%t A290470 Table[2 Cos[n Pi/2] - RootSum[-1 + # + #^2 + #^3 &, #^n &] +
%t A290470 RootSum[1 - 2 #^2 - 2 #^3 + #^4 &, #^n &], {n, 20}]
%t A290470 LinearRecurrence[{1, 2, 6, 2, 2, -2, -2, -1, 1}, {3, 7, 15, 59, 143, 367, 1039, 2755, 7395}, 20]
%t A290470 CoefficientList[Series[-(((1 + x) (-3 - x - x^2 + x^3) (-1 - 4 x^3 + 3 x^4))/((1 + x^2) (-1 - x - x^2 + x^3) (1 - 2 x - 2 x^2 + x^4))), {x, 0, 20}], x]
%o A290470 (PARI) Vec((1 + x)*(1 + 4*x^3 - 3*x^4)*(3 + x + x^2 - x^3)/((1 + x^2)*(1 + x + x^2 - x^3)*(1 - 2*x - 2*x^2 + x^4)) + O(x^30)) \\ _Andrew Howroyd_, Aug 04 2017
%Y A290470 Cf. A020866, A020877, A020878, A284710.
%K A290470 nonn
%O A290470 1,1
%A A290470 _Eric W. Weisstein_, Aug 03 2017
%E A290470 a(1)-a(2) and terms a(9) and beyond from _Andrew Howroyd_, Aug 04 2017