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 A387481 #14 Sep 01 2025 06:55:24
%S A387481 1,0,3,6,9,72,63,486,1053,2808,11907,22518,99225,246888,755487,
%T A387481 2554902,6488829,23112216,63506835,198653958,623336553,1781565192,
%U A387481 5807475711,16898655942,52699192029,161995971384,484990399395,1525112887446,4572778238649,14184781485480,43472894580063
%N A387481 a(n) = Sum_{k=0..floor(n/2)} 3^k * 2^(n-2*k) * binomial(k,n-2*k)^2.
%H A387481 Vincenzo Librandi, <a href="/A387481/b387481.txt">Table of n, a(n) for n = 0..1000</a>
%F A387481 G.f.: 1/sqrt((1-3*x^2-6*x^3)^2 - 72*x^5).
%t A387481 Table[Sum[3^k * 2^(n-2*k)*Binomial[k,n-2*k]^2,{k,0,Floor[n/2]}],{n,0,40}] (* _Vincenzo Librandi_, Sep 01 2025 *)
%o A387481 (PARI) a(n) = sum(k=0, n\2, 3^k*2^(n-2*k)*binomial(k, n-2*k)^2);
%o A387481 (Magma) [(&+[3^k * 2^(n-2*k)* Binomial(k,n-2*k)^2: k in [0..Floor(n/2)]]): n in [0..40]]; // _Vincenzo Librandi_, Sep 01 2025
%Y A387481 Cf. A387480, A387482.
%K A387481 nonn,new
%O A387481 0,3
%A A387481 _Seiichi Manyama_, Aug 30 2025