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 A174565 #13 Oct 02 2023 14:34:21 %S A174565 1,1,-3,9,-11,1,45,-135,229,-143,-483,2025,-4139,4321,3597,-28071, %T A174565 69829,-97199,12285,351945,-1104971,1907137,-1301523,-3723975, %U A174565 16378021,-34238159,37202397,25345449,-224845931,573156001,-820084275,167628825,2777450629,-9002867183 %N A174565 Expansion of g.f. (1+3*x)/((1-x)*(1+3*x+4*x^2)). %C A174565 Bisection of A107443. %H A174565 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (-2, -1, 4). %F A174565 a(n) = (1/2)*(1 - A087168(n+1)). %o A174565 (Magma) a087168:=func< n | &+[ Binomial(n+k, 2*k)*(-2)^(n-k): k in [0..n] ] >; [ (1-a087168(n+1))/2: n in [0..35] ]; %K A174565 sign,easy %O A174565 0,3 %A A174565 _Ralf Stephan_, Nov 29 2010