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 A290587 #24 Feb 16 2025 08:33:49
%S A290587 3,16,81,265,729,1786,4060,8833,18786,39586,83273,175463,370615,
%T A290587 784290,1661122,3517669,7441936,15720066,33145015,69744491,146458013,
%U A290587 306933394,642004440,1340415817,2793811726,5813791138,12080174037,25065845455,51943066643,107509343618,222265656670,459025904205,947041760092,1952064327682
%N A290587 Number of irredundant sets in the n-Andrásfai graph.
%H A290587 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/AndrasfaiGraph.html">Andrásfai Graph</a>
%H A290587 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/IrredundantSet.html">Irredundant Set</a>
%H A290587 <a href="/index/Rec#order_08">Index entries for linear recurrences with constant coefficients</a>, signature (10, -43, 104, -155, 146, -85, 28, -4).
%F A290587 From _Eric W. Weisstein_, Aug 21 2017: (Start)
%F A290587 a(n) = (-45*(8 + 3*2^n) + (1772 + 405*2^n) n - 1010*n^2 + 25*n^3 + 50*n^4 + 3*n^5)/120 for n > 3.
%F A290587 a(n) = 10*a(n-1) - 43*a(n-2) + 104*a(n-3) - 155*a(n-4) + 146*a(n-5) - 85*a(n-6) + 28*a(n-7) - 4*a(n-8) for n > 11.
%F A290587 G.f.: -((x (-3 + 14 x - 50 x^2 + 169 x^3 - 363 x^4 + 491 x^5 - 461 x^6 + 260 x^7 - 46 x^8 - 22 x^9 + 8 x^10))/((-1 + x)^6 (-1 + 2 x)^2)).
%F A290587 (End)
%t A290587 Table[Piecewise[{{3, n == 1}, {16, n == 2}, {81, n == 3}}, (-45 (8 + 3 2^n) + (1772 + 405 2^n) n - 1010 n^2 + 25 n^3 + 50 n^4 + 3 n^5)/120], {n, 20}] (* _Eric W. Weisstein_, Aug 21 2017 *)
%t A290587 Join[{3, 16, 81}, LinearRecurrence[{10, -43, 104, -155, 146, -85, 28, -4}, {265, 729, 1786, 4060, 8833, 18786, 39586, 83273}, 20]] (* _Eric W. Weisstein_, Aug 21 2017 *)
%t A290587 CoefficientList[Series[-((-3 + 14 x - 50 x^2 + 169 x^3 - 363 x^4 + 491 x^5 - 461 x^6 + 260 x^7 - 46 x^8 - 22 x^9 + 8 x^10)/((-1 + x)^6 (-1 + 2 x)^2)), {x, 0, 20}], x] (* _Eric W. Weisstein_, Aug 21 2017 *)
%Y A290587 Cf. A285272, A286879, A291053.
%K A290587 nonn
%O A290587 1,1
%A A290587 _Eric W. Weisstein_, Aug 07 2017
%E A290587 a(9)-a(20) from _Andrew Howroyd_, Aug 19 2017
%E A290587 a(21) and above from _Eric W. Weisstein_, Aug 21 2017