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 A379684 #8 Dec 30 2024 02:17:00
%S A379684 1,0,3,11,193,2389,50191,1088205,29836353,902845673,31428924631,
%T A379684 1207426391137,51394833121105,2386048646491197,120379283952129567,
%U A379684 6547887322803355589,382306453347573490177,23839225109022069540817,1581540933047988924532135
%N A379684 Expansion of e.g.f. (1/x) * Series_Reversion( x * exp(x) * (1 - x*exp(x)) ).
%F A379684 a(n) = (1/(n+1)) * Sum_{k=0..n} (-k-1)^k * (2*n-k)!/(k! * (n-k)!).
%o A379684 (PARI) a(n) = sum(k=0, n, (-k-1)^k*(2*n-k)!/(k!*(n-k)!))/(n+1);
%Y A379684 Cf. A213644, A377890, A379685.
%K A379684 nonn
%O A379684 0,3
%A A379684 _Seiichi Manyama_, Dec 29 2024