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 A352659 #12 Apr 06 2022 11:46:30
%S A352659 1,1,2,7,28,140,841,5887,47096,423865,4238650,46625150,559501801,
%T A352659 7273523413,101829327782,1527439916731,24439038667696,415463657350832,
%U A352659 7478345832314977,142088570813984563,2841771416279691260,59677199741873516461,1312898394321217362142
%N A352659 a(n) = n! * Sum_{k=0..floor(n/3)} 1 / (3*k)!.
%H A352659 Seiichi Manyama, <a href="/A352659/b352659.txt">Table of n, a(n) for n = 0..449</a>
%F A352659 E.g.f.: (exp(x) + 2 * exp(-x/2) * cos(sqrt(3)*x/2)) / (3*(1 - x)).
%F A352659 a(n) = floor(c * n!), where c = 1.16805831... = A143819.
%t A352659 Table[n! Sum[1/(3 k)!, {k, 0, Floor[n/3]}], {n, 0, 22}]
%t A352659 nmax = 22; CoefficientList[Series[(Exp[x] + 2 Exp[-x/2] Cos[Sqrt[3] x/2])/(3 (1 - x)), {x, 0, nmax}], x] Range[0, nmax]!
%o A352659 (PARI) a(n) = n! * sum(k=0, n\3, 1/(3*k)!); \\ _Michel Marcus_, Mar 29 2022
%Y A352659 Cf. A000522, A009179, A087350, A143819, A348597, A352660.
%K A352659 nonn
%O A352659 0,3
%A A352659 _Ilya Gutkovskiy_, Mar 25 2022