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 A379846 #12 Feb 05 2025 09:22:35
%S A379846 1,2,15,202,3993,104896,3449431,136490768,6319722513,335372124160,
%T A379846 20074806151551,1338341234648320,98356732036224745,
%U A379846 7900673166769620992,688709957632464564231,64754459774124307019776,6532479591772426224737697,703834470938326183482621952
%N A379846 Expansion of e.g.f. (1/x) * Series_Reversion( x * exp(-x) / (1 + x*exp(2*x)) ).
%F A379846 a(n) = (n!/(n+1)) * Sum_{k=0..n} (3*n-2*k+1)^k * binomial(n+1,n-k)/k!.
%F A379846 E.g.f. A(x) satisfies A(x) = exp(x*A(x)) / ( 1 - x*exp(3*x*A(x)) ). - _Seiichi Manyama_, Feb 04 2025
%o A379846 (PARI) a(n) = n!*sum(k=0, n, (3*n-2*k+1)^k*binomial(n+1, n-k)/k!)/(n+1);
%Y A379846 Cf. A088690, A379456, A379847.
%Y A379846 Cf. A366232, A379701.
%K A379846 nonn
%O A379846 0,2
%A A379846 _Seiichi Manyama_, Jan 04 2025