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 A091495 #19 Nov 21 2024 09:05:43
%S A091495 105,165,195,1155,1365,1785,1995,2145,2415,2805,3003,3045,3135,3255,
%T A091495 3315,3705,3795,3885,3927,4305,4389,4485,4515,4641,4785,4845,4935,
%U A091495 5115,5187,5313,5565,5655,5865,6045,6105,6195,6405,6555,6765,7035,7095,7215
%N A091495 Odd squarefree numbers k such that k/phi(k) > 2, where phi is Euler's totient function.
%C A091495 Apparently the squarefree members of the sequence A036798. Note that 105, 165 and 195 are the only terms having 3 prime factors. Also note that all the numbers listed above have 3 as a factor. The smallest number of this form not divisible by 3 is 37182145 = 5*7*11*13*17*19*23.
%C A091495 From _Amiram Eldar_, Nov 21 2024: (Start)
%C A091495 If k is term and m is an odd squarefree number coprime to k, then k*m is also a term.
%C A091495 The numbers of terms that do not exceed 10^k, for k = 3, 4, ..., are 3, 58, 513, 5108, 52365, 523975, 5214831, 52103339, 521507571, ... . Apparently, the asymptotic density of this sequence exists and equals 0.00521... . (End)
%H A091495 Amiram Eldar, <a href="/A091495/b091495.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1000 from T. D. Noe)
%t A091495 lst={}; Do[f=FactorInteger[n]; s=Times@@Last/@f; If[s==1&&Times@@(1-1/(First/@f))<1/2, AppendTo[lst, n]], {n, 3, 10000, 2}]; lst
%t A091495 Select[Range[1,7301,2],SquareFreeQ[#]&&#/EulerPhi[#]>2&] (* _Harvey P. Dale_, Jul 10 2017 *)
%o A091495 (PARI) is(k) = if(!(k%2), 0, my(f=factor(k)); issquarefree(f) && k / eulerphi(f) > 2); \\ _Amiram Eldar_, Nov 21 2024
%Y A091495 Cf. A000010, A036798, A056911, A118700.
%K A091495 nonn
%O A091495 1,1
%A A091495 _T. D. Noe_, Jan 15 2004