Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #11 Apr 16 2024 02:40:07
%S 2,3,5,7,13,31,37,61,181,241,421,1009,1201,1321,1801,2161,2521,7561,
%T 12601,15121,30241,55441,110881,278263,332641,555911,666917,722473,
%U 1443853,2165407,3607403,4324321,7212581,8654539,10817761,21631147,36768847,43243201,61276871
%N Numbers k > 1 such that sigma(phi(k))/sigma(k) > sigma(phi(j))/sigma(j) for all 1 < j < k.
%C Without the restrictions k > 1 and j > 1, 1 will be a term instead of 2 and 3. - _Amiram Eldar_, Apr 16 2024
%H Amiram Eldar, <a href="/A067573/b067573.txt">Table of n, a(n) for n = 1..53</a>
%t a = 0; Do[b = DivisorSigma[1, EulerPhi[n]]/DivisorSigma[1, n]; If[b > a, a = b; Print[n]], {n, 2, 10^7}]
%o (PARI) lista(kmax) = {my(rm = 0, f); for(k = 2, kmax, f = factor(k); r = sigma(eulerphi(f)) / sigma(f); if(r > rm, rm = r; print1(k, ", ")));} \\ _Amiram Eldar_, Apr 16 2024
%Y Cf. A000010 (phi), A000203 (sigma), A062402.
%K nonn
%O 1,1
%A _Robert G. Wilson v_, Jan 30 2002
%E a(37)-a(39) added and name corrected by _Amiram Eldar_, Apr 16 2024