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 A362156 #9 Apr 10 2023 10:51:45
%S A362156 -1,-1,1,5,9,11,17,59,237,849,2861,9625,33057,115753,410581,1469325,
%T A362156 5296449,19216691,70134489,257320475,948545125,3511308899,13047504065,
%U A362156 48649662439,181967395749,682578873479,2567177040641,9678602093387,36571567691029
%N A362156 Expansion of -1/(1 - x * sqrt(1-4*x)).
%F A362156 a(n) = -Sum_{k=0..n} (-4)^k * binomial((n-k)/2,k).
%o A362156 (PARI) my(N=30, x='x+O('x^N)); Vec(-1/(1-x*sqrt(1-4*x)))
%Y A362156 Cf. A000984, A362157.
%K A362156 sign,easy
%O A362156 0,4
%A A362156 _Seiichi Manyama_, Apr 09 2023