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 A362161 #11 Apr 10 2023 10:51:57
%S A362161 1,-1,5,-1,121,1039,20221,416975,10573361,309650399,10335294901,
%T A362161 386839539679,16045117551145,730346985279599,36191355037097261,
%U A362161 1939288174467052079,111724538085236200801,6886112439557645126335,452112545350761238085221
%N A362161 Expansion of e.g.f. exp(-x * sqrt(1-4*x)).
%F A362161 a(n) = (-1)^n * n! * Sum_{k=0..n} 4^k * binomial((n-k)/2,k)/(n-k)!.
%F A362161 a(n) ~ 2^(2*n - 5/2) * n^(n-1) / exp(n). - _Vaclav Kotesovec_, Apr 10 2023
%o A362161 (PARI) my(N=20, x='x+O('x^N)); Vec(serlaplace(exp(-x*sqrt(1-4*x))))
%Y A362161 Cf. A362158.
%K A362161 sign,easy
%O A362161 0,3
%A A362161 _Seiichi Manyama_, Apr 10 2023