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 A292542 #9 Feb 16 2025 08:33:51
%S A292542 3,39,156,624,2496,9984,39936,159744,638976,2555904,10223616,40894464,
%T A292542 163577856,654311424,2617245696,10468982784,41875931136,167503724544,
%U A292542 670014898176,2680059592704,10720238370816,42880953483264,171523813933056,686095255732224
%N A292542 Number of 4-cycles in the n-Sierpinski tetrahedron graph.
%H A292542 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/GraphCycle.html">Graph Cycle</a>
%H A292542 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/SierpinskiTetrahedronGraph.html">Sierpinski Tetrahedron Graph</a>
%H A292542 <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (4).
%F A292542 a(n) = 39*4^(n - 2) for n > 1.
%F A292542 a(n) = 4*a(n-1) for n > 2.
%F A292542 G.f.: -3*x*(1 + 9*x)/(-1 + 4*x).
%t A292542 Table[If[n == 1, 3, 39 4^(n - 1)], {n, 30}]
%t A292542 Join[{3}, LinearRecurrence[{4}, {39}, 20]]
%t A292542 CoefficientList[Series[-3 (1 + 9 x)/(-1 + 4 x), {x, 0, 20}], x]
%Y A292542 Cf. A292540 (3-cycles), A292543 (5-cycles), A292545 (6-cycles).
%K A292542 nonn,easy
%O A292542 1,1
%A A292542 _Eric W. Weisstein_, Sep 18 2017