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 A351941 #5 Feb 26 2022 10:53:02
%S A351941 1,-1,1,0,-3,8,-3,-57,225,-96,-2991,13873,-255,-313506,1495089,
%T A351941 1473024,-54621231,243365688,705129201,-14109279483,53228648865,
%U A351941 349791931434,-5000315242479,13572033641204,204954070915977,-2294997521498172,2691551249257017
%N A351941 a(0) = 1; a(n) = -Sum_{k=0..floor((n-1)/2)} binomial(n-1,2*k) * a(k) * a(n-2*k-1).
%F A351941 E.g.f.: exp( -Sum_{n>=0} a(n) * x^(2*n+1) / (2*n+1)! ).
%t A351941 a[0] = 1; a[n_] := a[n] = -Sum[Binomial[n - 1, 2 k] a[k] a[n - 2 k - 1], {k, 0, Floor[(n - 1)/2]}]; Table[a[n], {n, 0, 26}]
%Y A351941 Cf. A101912, A138314.
%K A351941 sign
%O A351941 0,5
%A A351941 _Ilya Gutkovskiy_, Feb 26 2022