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 A365121 #13 Dec 06 2024 06:59:38
%S A365121 1,3,9,40,192,993,5375,30081,172650,1010640,6010530,36214656,
%T A365121 220590082,1356131892,8403647454,52436122717,329170499604,
%U A365121 2077465903503,13173914483799,83897445169341,536355204428412,3440875097256529,22144300030907667
%N A365121 G.f. A(x) satisfies A(x) = (1 + x / (1 - x*A(x))^2)^3.
%F A365121 If g.f. satisfies A(x) = (1 + x/(1 - x*A(x))^s)^t, then a(n) = Sum_{k=0..n} binomial(t*(n-k+1),k) * binomial(n+(s-1)*k-1,n-k)/(n-k+1).
%F A365121 G.f.: A(x) = B(x)^3 where B(x) is the g.f. of A367242. - _Seiichi Manyama_, Dec 06 2024
%o A365121 (PARI) a(n, s=2, t=3) = sum(k=0, n, binomial(t*(n-k+1), k)*binomial(n+(s-1)*k-1, n-k)/(n-k+1));
%Y A365121 Cf. A000108, A365120.
%Y A365121 Cf. A365119, A365122.
%Y A365121 Cf. A367242.
%K A365121 nonn
%O A365121 0,2
%A A365121 _Seiichi Manyama_, Aug 22 2023