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 A290707 #15 Mar 06 2025 20:14:14
%S A290707 1,4,11,24,47,88,163,304,575,1104,2147,4216,8335,16552,32963,65760,
%T A290707 131327,262432,524611,1048936,2097551,4194744,8389091,16777744,
%U A290707 33555007,67109488,134218403,268436184,536871695,1073742664,2147484547,4294968256,8589935615
%N A290707 a(n) = 2^(n+1) + n^2 - 1.
%C A290707 For n > 1, also the number of irredundant sets in the complete bipartite graph K_{n,n}.
%C A290707 For n > 1, also the number of irredundant sets in the 2 X n rook graph. - _Andrew Howroyd_, Aug 11 2017
%H A290707 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/CompleteBipartiteGraph.html">Complete Bipartite Graph</a>.
%H A290707 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/IrredundantSet.html">Irredundant Set</a>.
%H A290707 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (5,-9,7,-2).
%F A290707 a(n) = 2^(n+1) + n^2 - 1.
%F A290707 a(n) = 5*a(n-1) - 9*a(n-2) + 7*a(n-3) - 2*a(n-4).
%F A290707 G.f.: x*(1 - x - 2*x^3)/((-1 + x)^3*(-1 + 2*x)).
%F A290707 E.g.f.: exp(x)*(x^2 + x - 1 + 2*exp(x)). - _Elmo R. Oliveira_, Mar 06 2025
%t A290707 Table[2^(n + 1) + n^2 - 1, {n, 0, 40}]
%t A290707 LinearRecurrence[{5, -9, 7, -2}, {4, 11, 24, 47}, {0, 20}]
%t A290707 CoefficientList[Series[(1 - x - 2 x^3)/((-1 + x)^3 (-1 + 2 x)), {x, 0, 20}], x]
%o A290707 (PARI) a(n)=2^(n+1)+n^2-1 \\ _Charles R Greathouse IV_, Aug 09 2017
%Y A290707 Cf. A290709, A290818.
%K A290707 nonn,easy
%O A290707 0,2
%A A290707 _Eric W. Weisstein_, Aug 09 2017