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 A358604 #14 Nov 28 2022 12:05:24
%S A358604 1,1,1,0,-1,-2,-1,2,7,8,-1,-26,-49,-28,103,314,359,-344,-2113,-3682,
%T A358604 -161,14684,36791,25762,-100297,-373456,-472241,587846,3877487,
%U A358604 7149988,-1111801,-40808566,-103472249,-56751688,424662623,1490284654,1674543359,-4121143444
%N A358604 a(n) = Sum_{k=0..floor(n/3)} (-1)^k * (n-2*k)!/(n-3*k)!.
%H A358604 Seiichi Manyama, <a href="/A358604/b358604.txt">Table of n, a(n) for n = 0..1000</a>
%F A358604 a(n) = (2 * a(n-1) - n * a(n-3) + 1)/3 for n > 2.
%o A358604 (PARI) a(n) = sum(k=0, n\3, (-1)^k*(n-2*k)!/(n-3*k)!);
%Y A358604 Cf. A358603, A358605, A358606.
%Y A358604 Cf. A357532.
%K A358604 sign
%O A358604 0,6
%A A358604 _Seiichi Manyama_, Nov 23 2022