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 A290391 #10 Feb 16 2025 08:33:49
%S A290391 0,0,0,0,0,0,30,120,294,552,894,1320,1830,2424,3102,3864,4710,5640,
%T A290391 6654,7752,8934,10200,11550,12984,14502,16104,17790,19560,21414,23352,
%U A290391 25374,27480,29670,31944,34302,36744,39270,41880,44574,47352,50214,53160,56190,59304,62502
%N A290391 Number of 5-cycles in the n-triangular honeycomb obtuse knight graph.
%H A290391 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/GraphCycle.html">Graph Cycle</a>
%H A290391 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3, -3, 1).
%F A290391 For n >= 7, a(n) = 6*(292 - 90*n + 7*n^2).
%F A290391 For n >= 10, a(n) = 3*a(n-1)-3*a(n-2)+a(n-3).
%F A290391 G.f.: -6*x^7*(5 + 5*x + 4*x^2)/(-1 + x)^3.
%t A290391 Table[If[n < 7, 0, 6 (292 - 90 n + 7 n^2)], {n, 20}]
%t A290391 Join[{0, 0, 0, 0, 0, 0}, LinearRecurrence[{3, -3, 1}, {30, 120, 294}, 14]]
%t A290391 CoefficientList[Series[-((6 x^6 (5 + 5 x + 4 x^2))/(-1 + x)^3), {x, 0, 20}], x]
%Y A290391 Cf. A001105 (3-cycles in the triangular honeycomb obtuse knight graph), A194715 (4-cycles), A290392 (6-cycles).
%K A290391 nonn,easy
%O A290391 1,7
%A A290391 _Eric W. Weisstein_, Jul 29 2017