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 A356828 #11 Feb 16 2025 08:34:03
%S A356828 0,2,23,147,748,3414,14719,61495,252364,1024938,4137207,16639339,
%T A356828 66775964,267631726,1071801407,4290282671,17168559452,68692172578,
%U A356828 274811988823,1099352487299,4397662311948,17591258505542,70366504900671,281469570617703,1125886855379628
%N A356828 Number of vertex cuts in the n-ladder graph P_2 x P_n.
%H A356828 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/LadderGraph.html">Ladder Graph</a>
%H A356828 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/VertexCut.html">Vertex Cut</a>
%H A356828 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (8,-20,16,1,-4).
%F A356828 a(n) = 4^n + 2*n + (10 - LucasL(n + 3, 2))/4.
%F A356828 a(n) = 8*a(n-1) - 20*a(n-2) + 16*a(n-3) + a(n-4) - 4*a(n-5).
%F A356828 G.f.: x^2*(2+x)*(1+3*x)/((-1+x)^2*(-1+4*x)*(-1+2*x + x^2)).
%F A356828 a(n) = 2^(2*n) - A059020(n) - 1. - _Pontus von Brömssen_, Aug 30 2022
%t A356828 Table[4^n + 2 n + (10 - LucasL[n + 3, 2])/4, {n, 20}]
%t A356828 LinearRecurrence[{8, -20, 16, 1, -4}, {0, 2, 23, 147, 748}, 20]
%t A356828 CoefficientList[Series[x (2 + x) (1 + 3 x)/((-1 + x)^2 (-1 + 4 x) (-1 + 2 x + x^2)), {x, 0, 20}], x]
%Y A356828 Cf. A059020.
%K A356828 nonn,easy
%O A356828 1,2
%A A356828 _Eric W. Weisstein_, Aug 30 2022