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 A291706 #10 Feb 16 2025 08:33:51
%S A291706 3,9,24,56,136,328,792,1912,4616,11144,26904,64952,156808,378568,
%T A291706 913944,2206456,5326856,12860168,31047192,74954552,180956296,
%U A291706 436867144,1054690584,2546248312,6147187208,14840622728,35828432664,86497488056,208823408776,504144305608
%N A291706 Number of connected dominating sets in the n-ladder graph.
%H A291706 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/ConnectedDominatingSet.html">Connected Dominating Set</a>
%H A291706 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/LadderGraph.html">Ladder Graph</a>
%H A291706 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (2, 1).
%F A291706 a(n) = 4 lucas(n - 1, 2) for n > 2.
%F A291706 a(n) = 2*a(n-1) + a(n-2) for n > 4.
%F A291706 G.f.: (x (-3 - 3 x - 3 x^2 + x^3))/(-1 + 2 x + x^2).
%t A291706 Table[Piecewise[{{3^n, n == 1 || n == 2}}, 4 LucasL[n - 1, 2]], {n, 20}]
%t A291706 Join[{3, 9}, LinearRecurrence[{2, 1}, {24, 56}, 20]]
%t A291706 CoefficientList[Series[(-3 - 3 x - 3 x^2 + x^3)/(-1 + 2 x + x^2), {x, 0, 20}], x]
%Y A291706 Row 2 of A291872.
%K A291706 nonn,easy
%O A291706 1,1
%A A291706 _Eric W. Weisstein_, Aug 30 2017