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 A317926 #11 May 09 2025 10:19:35
%S A317926 1,2,1,8,1,2,1,16,2,1,1,8,1,2,1,128,1,4,1,4,1,2,1,16,1,1,2,8,1,1,1,
%T A317926 256,1,1,1,16,1,2,1,8,1,2,1,8,1,2,1,128,2,1,1,4,1,4,1,16,1,1,1,4,1,2,
%U A317926 2,1024,1,2,1,1,1,1,1,32,1,1,1,8,1,1,1,64,8,1,1,8,1,2,1,16,1,2,1,8,1,2,1,256,1,4,2,1,1,1,1,8,1
%N A317926 Denominators of rational valued sequence whose Dirichlet convolution with itself yields Euler's phi (A000010).
%H A317926 Antti Karttunen, <a href="/A317926/b317926.txt">Table of n, a(n) for n = 1..16384</a>
%F A317926 a(n) = denominator of f(n), where f(1) = 1, f(n) = (1/2) * (A000010(n) - Sum_{d|n, d>1, d<n} f(d) * f(n/d)) for n > 1.
%t A317926 f[1] = 1; f[n_] := f[n] = (EulerPhi[n] - DivisorSum[n, f[#]*f[n/#] &, 1 < # < n &])/2; Denominator @ Array[f, 100] (* _Amiram Eldar_, Dec 12 2022 *)
%o A317926 (PARI)
%o A317926 A317925perA317926(n) = if(1==n,n,(eulerphi(n)-sumdiv(n,d,if((d>1)&&(d<n),A317925perA317926(d)*A317925perA317926(n/d),0)))/2);
%o A317926 A317926(n) = denominator(A317925perA317926(n));
%o A317926 (PARI) for(n=1, 100, print1(denominator(direuler(p=2, n, ((1-X)/(1-p*X))^(1/2))[n]), ", ")) \\ _Vaclav Kotesovec_, May 09 2025
%Y A317926 Cf. A000010, A317925 (numerators).
%Y A317926 Cf. also A046644, A317832.
%K A317926 nonn,frac
%O A317926 1,2
%A A317926 _Antti Karttunen_, Aug 11 2018