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 A378555 #13 Nov 30 2024 09:50:09
%S A378555 1,1,9,19,305,156,13233,-23988,688113,-2863070,41085704,-246536784,
%T A378555 2696513885,-19410931916,187672944300,-1481383572516,13522625165601,
%U A378555 -111877103550195,994511499413664,-8430550720540365,74061353032540020,-636000265949289978
%N A378555 a(n) = Sum_{k=0..n} 9^(n-k) * binomial(n+k-1,k) * binomial(k/3,n-k).
%F A378555 a(n) = [x^n] 1/(1 - x*(1 + 9*x)^(1/3))^n.
%t A378555 a[n_]:=SeriesCoefficient[1/(1 - x*(1 + 9*x)^(1/3))^n,{x,0,n}]; Array[a,22,0] (* _Stefano Spezia_, Nov 30 2024 *)
%o A378555 (PARI) a(n) = sum(k=0, n, 9^(n-k)*binomial(n+k-1, k)*binomial(k/3, n-k));
%Y A378555 Cf. A213684, A378554.
%Y A378555 Cf. A372126.
%K A378555 sign
%O A378555 0,3
%A A378555 _Seiichi Manyama_, Nov 30 2024