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 A357821 #8 Oct 15 2022 07:21:58
%S A357821 1,3,12,4,12,6,24,8,24,72,72,18,63,504,63,504,168,504,2520,2520,10080,
%T A357821 1120,3360,3360,672,224,2016,2016,10080,10080,5040,2520,5040,15120,
%U A357821 1890,7560,143640,143640,17955,143640,143640,574560,6320160,6320160,6320160,6320160
%N A357821 Denominators of the partial alternating sums of the reciprocals of the Dedekind psi function (A001615).
%C A357821 See A357820 for more details.
%F A357821 a(n) = denominator(Sum_{k=1..n} (-1)^(k+1)/psi(k)).
%t A357821 psi[n_] := n * Times @@ (1 + 1/Transpose[FactorInteger[n]][[1]]); psi[1] = 1; Denominator[Accumulate[1/Array[(-1)^(# + 1)*psi[#] &, 50]]]
%o A357821 (PARI) f(n) = n * sumdivmult(n, d, issquarefree(d)/d); \\ A001615
%o A357821 a(n) = denominator(sum(k=1, n, (-1)^(k+1)/f(k))); \\ _Michel Marcus_, Oct 15 2022
%Y A357821 Cf. A001615, A173290, A357820 (numerators).
%Y A357821 Similar sequence: A211178.
%K A357821 nonn,frac
%O A357821 1,2
%A A357821 _Amiram Eldar_, Oct 14 2022