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 A164646 #8 Jun 22 2019 14:44:06
%S A164646 51,477,595,3567,17765,20735,41615,104931,276651,470721,493493,599169,
%T A164646 834591,993395,1092845,1242505,1318521,1479981,1490645,1712037,
%U A164646 2344045,2736305,2912463,2986941,2990709,3042873,3187917,3277611,3295821,3767331,4686039,5059881
%N A164646 Numbers n such that sigma(n)/phi(n) = 9/4.
%C A164646 A subsequence of A011257.
%C A164646 If 3^{k+1}-1 = d*D such that p = 2*b^{k+1}*(d+1) - 1 and q = 2*(b^{k+1}+D)-1 are distinct primes, then n = 3^k*p*q is a term of this sequence.
%C A164646 The same theorem holds for sequences of numbers such that sigma/phi=b^2/(b-1)^2 with other primes b (here b=3; in A068390: b=2, in A164648: b=5).
%H A164646 Donovan Johnson, <a href="/A164646/b164646.txt">Table of n, a(n) for n = 1..1000</a>
%t A164646 Select[Range[506*10^4],DivisorSigma[1,#]/EulerPhi[#]==9/4&] (* _Harvey P. Dale_, Jun 22 2019 *)
%o A164646 (PARI) for( n=1,1e7, sigma(n)==9/4*eulerphi(n) && print1(n","))
%Y A164646 Cf. A000010 (=phi), A000203 (=sigma), A068390 (sigma/phi=4), A163667 (sigma/phi=9), A164647 (sigma/phi=16/9).
%K A164646 nonn
%O A164646 1,1
%A A164646 _M. F. Hasler_, Aug 22 2009