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 A341549 #18 Feb 15 2021 22:36:10
%S A341549 3,6,23,50,131,294,687,1530,3419,7502,16391,35490,76467,163830,349535,
%T A341549 742730,1572875,3320478,6990519,14680050,30758243,64312646,134217743,
%U A341549 279620250,581610171,1207959534,2505397607,5189752130,10737418259,22190664342
%N A341549 a(n) = Sum_{k=1..n} (-1)^(n+k)*A087322(n,k).
%H A341549 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (3,1,-7,0,4).
%F A341549 a(n) = ((n + 1)*2^(n + 2) - 3 + (4*n + 1)*(-1)^(n + 1))/6.
%F A341549 G.f.: (4*x^3 - 2*x^2 + 3*x - 3)*x/((-1 + 2*x)^2*(-1 + x)*(1 + x)^2).
%Y A341549 Cf. A087322.
%K A341549 nonn,easy
%O A341549 1,1
%A A341549 _Petros Hadjicostas_, Feb 15 2021