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 A380723 #11 Jan 31 2025 09:25:34
%S A380723 1,2,21,436,13785,589206,31825381,2080523880,159761186577,
%T A380723 14097898530730,1405926737063541,156379679761925148,
%U A380723 19195200442017128425,2577494115099820986174,375845854490491567916805,59145488004443221188738256,9990898494797767848442559649,1803160967691789114062089511250
%N A380723 E.g.f. A(x) satisfies A(x) = exp(x * A(x)^2) / (1 - x*A(x)^2).
%F A380723 a(n) = n! * Sum_{k=0..n} (2*n+1)^(k-1) * binomial(3*n-k,n-k)/k!.
%o A380723 (PARI) a(n) = n!*sum(k=0, n, (2*n+1)^(k-1)*binomial(3*n-k, n-k)/k!);
%Y A380723 Cf. A377831, A380724.
%Y A380723 Cf. A371318, A377888.
%Y A380723 Cf. A360601, A380718.
%K A380723 nonn
%O A380723 0,2
%A A380723 _Seiichi Manyama_, Jan 30 2025