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 A354378 #7 May 25 2022 09:08:14
%S A354378 1,2,24,720,8064,3628800,479001600,87178291200,20922789888000,
%T A354378 1280474741145600,2432902008176640000,1124000727777607680000,
%U A354378 620448401733239439360000,403291461126605635584000000,60977668922342772100300800000,1569543549184562477137920000000
%N A354378 a(n) is the denominator of Sum_{k=0..n} (-1)^k / (2*k)!.
%F A354378 Denominators of coefficients in expansion of cos(sqrt(x)) / (1 - x).
%e A354378 1, 1/2, 13/24, 389/720, 4357/8064, 1960649/3628800, 258805669/479001600, ...
%t A354378 Table[Sum[(-1)^k/(2 k)!, {k, 0, n}], {n, 0, 15}] // Denominator
%t A354378 nmax = 15; CoefficientList[Series[Cos[Sqrt[x]]/(1 - x), {x, 0, nmax}], x] // Denominator
%o A354378 (PARI) a(n) = denominator(sum(k=0, n, (-1)^k/(2*k)!)); \\ _Michel Marcus_, May 24 2022
%Y A354378 Cf. A010050, A049470, A053556, A061355, A143383, A354138 (numerators), A354331, A354333, A354335.
%K A354378 nonn,frac
%O A354378 0,2
%A A354378 _Ilya Gutkovskiy_, May 24 2022