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 A371139 #15 Sep 19 2024 14:43:15
%S A371139 1,0,0,6,12,20,2190,17682,94136,4762872,83210490,920248670,
%T A371139 34266719652,948535937076,17568958623398,607198057666410,
%U A371139 22018456385103600,595499717140604912,21682086461493768306,926586132659265073590,33197900968981072951580
%N A371139 E.g.f. satisfies A(x) = 1 + x^2*A(x)^2*(exp(x*A(x)) - 1).
%H A371139 <a href="/index/Res#revert">Index entries for reversions of series</a>
%F A371139 a(n) = (n!)^2 * Sum_{k=0..floor(n/3)} Stirling2(n-2*k,k)/( (n-2*k)! * (n-k+1)! ).
%F A371139 E.g.f.: (1/x) * Series_Reversion( x/(1 + x^2*(exp(x) - 1)) ). - _Seiichi Manyama_, Sep 19 2024
%o A371139 (PARI) a(n) = n!^2*sum(k=0, n\3, stirling(n-2*k, k, 2)/((n-2*k)!*(n-k+1)!));
%Y A371139 Cf. A000272, A371119, A376293.
%K A371139 nonn
%O A371139 0,4
%A A371139 _Seiichi Manyama_, Mar 12 2024