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 A352280 #15 Feb 18 2025 08:56:36
%S A352280 1,3,9,30,117,516,2493,13152,75177,460272,3003921,20806176,152114013,
%T A352280 1169842368,9435180357,79553524224,699531782481,6400932102912,
%U A352280 60820145019801,599036357936640,6105903392066373,64309189153428480,698936466350352717,7828833281592926208,90270159223293364473
%N A352280 a(0) = 1; a(n) = 3 * Sum_{k=0..floor((n-1)/2)} binomial(n-1,2*k) * a(n-2*k-1).
%H A352280 Seiichi Manyama, <a href="/A352280/b352280.txt">Table of n, a(n) for n = 0..565</a>
%F A352280 E.g.f.: exp( 3 * sinh(x) ).
%F A352280 a(n) = Sum_{k=0..n} 3^k * A136630(n,k). - _Seiichi Manyama_, Feb 18 2025
%t A352280 a[0] = 1; a[n_] := a[n] = 3 Sum[Binomial[n - 1, 2 k] a[n - 2 k - 1], {k, 0, Floor[(n - 1)/2]}]; Table[a[n], {n, 0, 24}]
%t A352280 nmax = 24; CoefficientList[Series[Exp[3 Sinh[x]], {x, 0, nmax}], x] Range[0, nmax]!
%o A352280 (PARI) my(N=40, x='x+O('x^N)); Vec(serlaplace(exp(3*sinh(x)))) \\ _Seiichi Manyama_, Mar 26 2022
%Y A352280 Cf. A027710, A080527, A107403.
%Y A352280 Cf. A003724, A136630, A352279.
%K A352280 nonn
%O A352280 0,2
%A A352280 _Ilya Gutkovskiy_, Mar 10 2022