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 A379087 #9 Dec 15 2024 06:46:31
%S A379087 1,3,15,93,651,4803,36177,275208,2108091,16243671,125817345,978933354,
%T A379087 7646000421,59915086026,470820659940,3708756501018,29276677544619,
%U A379087 231540519752376,1834228504348863,14552075416977531,115605043235217081,919503729585453147
%N A379087 a(n) = Sum_{k=0..floor(n/3)} binomial(3*n+k-1,k) * binomial(3*n+k,n-3*k).
%F A379087 a(n) = [x^n] 1/( 1/(1 + x) - x^3 )^(3*n).
%F A379087 a(n) == 0 (mod 3) for n>0.
%o A379087 (PARI) a(n) = sum(k=0, n\3, binomial(3*n+k-1, k)*binomial(3*n+k, n-3*k));
%Y A379087 Cf. A379025, A379086.
%Y A379087 Cf. A379090.
%K A379087 nonn
%O A379087 0,2
%A A379087 _Seiichi Manyama_, Dec 15 2024