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 A380801 #8 Feb 04 2025 08:59:47
%S A380801 1,2,16,206,3792,91402,2733376,97793334,4078001920,194355934802,
%T A380801 10426538225664,621994665546718,40852668904155136,2929900797265945050,
%U A380801 227853412116442243072,19100256246157081925318,1716982264495843606462464,164771462679434867316243874
%N A380801 Expansion of e.g.f. ( (1/x) * Series_Reversion( x * exp(-x / (1 - x)^2) ) )^2.
%H A380801 <a href="/index/Res#revert">Index entries for reversions of series</a>
%F A380801 E.g.f.: B(x)^2, where B(x) is the e.g.f. of A364939.
%F A380801 E.g.f. A(x) satisfies A(x) = exp( 2 * x * A(x)^(1/2) / (1 - x*A(x)^(1/2))^2 ).
%F A380801 a(n) = 2 * n! * Sum_{k=0..n} (n+2)^(k-1) * binomial(n+k-1,n-k)/k!.
%o A380801 (PARI) a(n, q=2, r=1, s=1, t=2, u=0) = q*n!*sum(k=0, n, (r*n+(s-r)*k+q)^(k-1)*binomial((r*u+1)*n+((s-r)*u+t-1)*k+q*u-1, n-k)/k!);
%Y A380801 Cf. A364939.
%K A380801 nonn
%O A380801 0,2
%A A380801 _Seiichi Manyama_, Feb 04 2025