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 A381880 #9 Mar 09 2025 12:29:00
%S A381880 1,4,27,223,2052,20199,208205,2219149,24261279,270581313,3066581130,
%T A381880 35216499786,408919039968,4792955710138,56633333886618,
%U A381880 673881539636365,8067939162382594,97117925556632184,1174721577627568371,14270877151754826473,174044527062280321368
%N A381880 Expansion of (1/x) * Series_Reversion( x * (1-x)^3 / C(x) ), where C(x) is the g.f. of A000108.
%F A381880 G.f. A(x) satisfies A(x) = C(x*A(x)) / (1 - x*A(x))^3.
%F A381880 a(n) = Sum_{k=0..n} binomial(n+2*k+1,k) * binomial(4*n-k+2,n-k)/(n+2*k+1).
%o A381880 (PARI) my(N=30, x='x+O('x^N)); Vec(serreverse(x*(1-x)^3*2*x/(1-sqrt(1-4*x)))/x)
%Y A381880 Cf. A381817, A381879.
%Y A381880 Cf. A000108, A381882.
%K A381880 nonn
%O A381880 0,2
%A A381880 _Seiichi Manyama_, Mar 09 2025