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 A362158 #8 Apr 10 2023 10:51:53
%S A362158 -1,-1,3,23,119,1119,19259,417143,10567983,309715199,10335277619,
%T A362158 386840046999,16045111426343,730346987476703,36191354975508459,
%U A362158 1939288175212058999,111724538084900577119,6886112439566787983103,452112545350650426838883
%N A362158 Expansion of e.g.f. -exp(x * sqrt(1-4*x)).
%F A362158 a(n) = - n! * Sum_{k=0..n} (-4)^k * binomial((n-k)/2,k)/(n-k)!.
%F A362158 a(n) ~ 2^(2*n - 5/2) * n^(n-1) / exp(n). - _Vaclav Kotesovec_, Apr 10 2023
%o A362158 (PARI) my(N=20, x='x+O('x^N)); Vec(serlaplace(-exp(x*sqrt(1-4*x))))
%Y A362158 Cf. A362156.
%K A362158 sign,easy
%O A362158 0,3
%A A362158 _Seiichi Manyama_, Apr 10 2023