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 A371742 #15 Apr 05 2024 13:06:56
%S A371742 1,3,16,92,551,3380,21065,132771,843944,5399802,34731776,224361283,
%T A371742 1454557294,9458829681,61670895633,403003997300,2638776935215,
%U A371742 17308508054848,113709379928689,748069400432262,4927608724973776,32495826854732633,214521754579553129
%N A371742 a(n) = Sum_{k=0..floor(n/2)} binomial(3*n-k,n-2*k).
%F A371742 a(n) = [x^n] 1/((1-x-x^2) * (1-x)^(2*n)).
%F A371742 a(n) ~ 3^(3*n + 3/2) / (5 * sqrt(Pi*n) * 2^(2*n)). - _Vaclav Kotesovec_, Apr 05 2024
%o A371742 (PARI) a(n) = sum(k=0, n\2, binomial(3*n-k, n-2*k));
%Y A371742 Cf. A108081, A371743, A371744.
%Y A371742 Cf. A066380, A371754.
%Y A371742 Cf. A183160.
%K A371742 nonn
%O A371742 0,2
%A A371742 _Seiichi Manyama_, Apr 05 2024