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 A371320 #7 Mar 19 2024 08:37:50
%S A371320 1,1,3,19,181,2341,38071,748567,17262505,457068745,13667029291,
%T A371320 455560747291,16750696633309,673549397276653,29403437531813983,
%U A371320 1384945157486054431,70010050730247746641,3780682522365453684625,217218502250130209410387
%N A371320 E.g.f. satisfies A(x) = exp(x) + x^2*A(x)^3.
%F A371320 a(n) = n! * Sum_{k=0..floor(n/2)} (2*k+1)^(n-2*k-1) * binomial(3*k,k)/(n-2*k)!.
%o A371320 (PARI) a(n) = n!*sum(k=0, n\2, (2*k+1)^(n-2*k-1)*binomial(3*k, k)/(n-2*k)!);
%Y A371320 Cf. A087208, A371319.
%K A371320 nonn
%O A371320 0,3
%A A371320 _Seiichi Manyama_, Mar 18 2024