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 A352649 #19 Jun 25 2025 06:31:57
%S A352649 1,3,18,171,2160,34035,643680,14203371,358178688,10161542691,
%T A352649 320315005440,11106766229163,420132741912576,17216605635562515,
%U A352649 759789379494512640,35925442734363182955,1811923104577065615360,97097117111612660889411,5509300889675218610552832
%N A352649 Expansion of e.g.f. 1/(1 - 3 * x * cosh(x)).
%F A352649 a(0) = 1; a(n) = 3 * Sum_{k=0..floor((n-1)/2)} (2*k+1) * binomial(n,2*k+1) * a(n-2*k-1).
%F A352649 a(n) = Sum_{k=0..n} 3^k * k! * A185951(n,k). - _Seiichi Manyama_, Jun 25 2025
%t A352649 With[{m = 17}, Range[0, m]! * CoefficientList[Series[1/(1 - 3*x*Cosh[x]), {x, 0, m}], x]] (* _Amiram Eldar_, Mar 26 2022 *)
%o A352649 (PARI) my(N=20, x='x+O('x^N)); Vec(serlaplace(1/(1-3*x*cosh(x))))
%o A352649 (PARI) a(n) = if(n==0, 1, 3*sum(k=0, (n-1)\2, (2*k+1)*binomial(n, 2*k+1)*a(n-2*k-1)));
%Y A352649 Cf. A205571, A352648.
%Y A352649 Cf. A185951.
%K A352649 nonn
%O A352649 0,2
%A A352649 _Seiichi Manyama_, Mar 25 2022