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 A352660 #12 Apr 06 2022 11:46:35
%S A352660 1,1,2,6,25,125,750,5250,42001,378009,3780090,41580990,498971881,
%T A352660 6486634453,90812882342,1362193235130,21795091762081,370516559955377,
%U A352660 6669298079196786,126716663504738934,2534333270094778681,53220998671990352301,1170861970783787750622
%N A352660 a(n) = n! * Sum_{k=0..floor(n/4)} 1 / (4*k)!.
%H A352660 Seiichi Manyama, <a href="/A352660/b352660.txt">Table of n, a(n) for n = 0..449</a>
%F A352660 E.g.f.: (cos(x) + cosh(x)) / (2*(1 - x)).
%F A352660 a(n) = floor(c * n!), where c = 1.04169147... = A332890.
%t A352660 Table[n! Sum[1/(4 k)!, {k, 0, Floor[n/4]}], {n, 0, 22}]
%t A352660 nmax = 22; CoefficientList[Series[(Cos[x] + Cosh[x])/(2 (1 - x)), {x, 0, nmax}], x] Range[0, nmax]!
%o A352660 (PARI) a(n) = n! * sum(k=0, n\4, 1/(4*k)!); \\ _Michel Marcus_, Mar 29 2022
%Y A352660 Cf. A000522, A009179, A332890, A337727, A349087, A352659.
%K A352660 nonn
%O A352660 0,3
%A A352660 _Ilya Gutkovskiy_, Mar 25 2022