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 A387480 #15 Sep 01 2025 07:12:32
%S A387480 1,3,15,99,603,3807,24759,162243,1072683,7147359,47887767,322330995,
%T A387480 2178055899,14765637663,100380161655,684061007139,4671543976587,
%U A387480 31962145170015,219043736154711,1503380943222867,10332034575214779,71092843087100319,489712662842798007
%N A387480 a(n) = Sum_{k=0..n} 3^k * 2^(n-k) * binomial(k,n-k)^2.
%H A387480 Vincenzo Librandi, <a href="/A387480/b387480.txt">Table of n, a(n) for n = 0..1000</a>
%F A387480 G.f.: 1/sqrt((1-3*x-6*x^2)^2 - 72*x^3).
%t A387480 Table[Sum[3^k*2^(n-k)*Binomial[k,n-k]^2,{k,0,n}],{n,0,25}] (* _Vincenzo Librandi_, Sep 01 2025 *)
%o A387480 (PARI) a(n) = sum(k=0, n, 3^k*2^(n-k)*binomial(k, n-k)^2);
%o A387480 (Magma) [&+[3^k * 2^(n-k) * Binomial(k, n-k)^2: k in [0..n]]: n in [0..25]]; // _Vincenzo Librandi_, Sep 01 2025
%Y A387480 Cf. A387481, A387482.
%Y A387480 Cf. A083858, A108490.
%K A387480 nonn,new
%O A387480 0,2
%A A387480 _Seiichi Manyama_, Aug 30 2025