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 A387648 #11 Sep 05 2025 10:29:07
%S A387648 1,0,0,1,2,0,1,12,4,1,30,60,9,56,280,225,106,840,1681,852,2012,7393,
%T A387648 8102,6116,24089,48288,39312,69889,206354,268496,264993,715868,
%U A387648 1419892,1498177,2407662,5980620,8659497,10078152,21975496,42559393,52699770,81920920,178653105
%N A387648 a(n) = Sum_{k=0..floor(n/3)} 2^(n-3*k) * binomial(2*k,2*n-6*k).
%H A387648 <a href="/index/Rec#order_08">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,2,4,0,-1,4,-4).
%F A387648 G.f.: (1-x^3-2*x^4)/((1-x^3-2*x^4)^2 - 8*x^7).
%F A387648 a(n) = 2*a(n-3) + 4*a(n-4) - a(n-6) + 4*a(n-7) - 4*a(n-8).
%o A387648 (PARI) a(n) = sum(k=0, n\3, 2^(n-3*k)*binomial(2*k, 2*n-6*k));
%Y A387648 Cf. A108480, A387647.
%K A387648 nonn,new
%O A387648 0,5
%A A387648 _Seiichi Manyama_, Sep 04 2025