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 A352278 #5 Mar 11 2022 02:10:57
%S A352278 1,-3,24,-273,3399,-31728,-280371,26388177,-580539936,-17406321933,
%T A352278 1809690920979,-18045563411208,-6249108953966151,333062472085204677,
%U A352278 27673022056089337224,-3800202930423874873353,-139584280492439116159521,52779027474493111545620352,279012844299708383976573189
%N A352278 a(0) = 1; a(n) = -3 * Sum_{k=1..n} binomial(2*n-1,2*k-1) * a(n-k).
%F A352278 E.g.f.: exp( 3 * (1 - cosh(x)) ) (even powers only).
%t A352278 a[0] = 1; a[n_] := a[n] = -3 Sum[Binomial[2 n - 1, 2 k - 1] a[n - k], {k, 1, n}]; Table[a[n], {n, 0, 18}]
%t A352278 nmax = 36; Take[CoefficientList[Series[Exp[3 (1 - Cosh[x])], {x, 0, nmax}], x] Range[0, nmax]!, {1, -1, 2}]
%Y A352278 Cf. A080527, A210676, A260884, A352277.
%K A352278 sign
%O A352278 0,2
%A A352278 _Ilya Gutkovskiy_, Mar 10 2022