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 A379086 #10 Dec 15 2024 06:45:11
%S A379086 1,3,21,174,1509,13443,121962,1120899,10401021,97230090,914283621,
%T A379086 8638552464,81945757734,779949538176,7444735446813,71237074583589,
%U A379086 683125330952205,6563268117869076,63164380112090814,608805362150884731,5875874727915635409,56780302474503539427,549294315060885105744
%N A379086 a(n) = Sum_{k=0..floor(n/2)} binomial(3*n+k-1,k) * binomial(3*n+k,n-2*k).
%F A379086 a(n) = [x^n] 1/( 1/(1 + x) - x^2 )^(3*n).
%F A379086 a(n) == 0 (mod 3) for n>0.
%o A379086 (PARI) a(n) = sum(k=0, n\2, binomial(3*n+k-1, k)*binomial(3*n+k, n-2*k));
%Y A379086 Cf. A379025, A379087.
%Y A379086 Cf. A379088.
%K A379086 nonn
%O A379086 0,2
%A A379086 _Seiichi Manyama_, Dec 15 2024