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 A367721 #8 Nov 28 2023 08:39:37
%S A367721 1,1,1,-5,-23,1,601,7771,26545,-401183,-6965999,-42828389,528611161,
%T A367721 15543020065,141983039017,-2393449681349,-83586615493919,
%U A367721 -708151768946879,15447932991283105,635290179334026427,7146984268771158601,-162583738763505944639
%N A367721 E.g.f. satisfies A(x) = exp(x*A(-x^2)).
%F A367721 a(0) = 1; a(n) = (n-1)! * Sum_{k=0..floor((n-1)/2)} (-1)^k * (2*k+1) * a(k) * a(n-1-2*k) / (k! * (n-1-2*k)!).
%o A367721 (PARI) a_vector(n) = my(v=vector(n+1)); v[1]=1; for(i=1, n, v[i+1]=(i-1)!*sum(j=0, (i-1)\2, (-1)^j*(2*j+1)*v[j+1]*v[i-2*j]/(j!*(i-1-2*j)!))); v;
%Y A367721 Cf. A141369, A367722, A367723.
%Y A367721 Cf. A138292.
%K A367721 sign
%O A367721 0,4
%A A367721 _Seiichi Manyama_, Nov 28 2023