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 #25 Dec 27 2024 04:12:02
%S 1,3,15,35,105,357,1045,1485,3135,3339,5049,10659,12441,16065,24871,
%T 24969,29029,33915,35343,39105,39585,50065,58435,64285,71145,74613,
%U 87087,87685,99693,124355,124605,132957,137885,140335,145145,150195
%N Odd integers m such that phi(m) | sigma(m).
%C Subsequence of A236693. Proof: if n is in this sequence, then 2^phi(n) - 1 is divisible by n and 2^sigma(n) - 1 is divisible by 2^phi(n) - 1. Therefore, 2^sigma(n) == 1 (mod n) and n is in A236693. - _Jinyuan Wang_, Mar 13 2020
%H Amiram Eldar, <a href="/A015715/b015715.txt">Table of n, a(n) for n = 1..10000</a> (calculated using data from Jud McCranie; terms 1..1000 from Donovan Johnson)
%t Select[Range[1,151001,2],Divisible[DivisorSigma[1,#],EulerPhi[#]]&] (* _Harvey P. Dale_, Sep 16 2016 *)
%o (PARI) isok(m) = (m % 2) && !(sigma(m) % eulerphi(m)); \\ _Michel Marcus_, Mar 14 2020
%Y Subsequence of A020492 and A236693.
%Y Cf. A000010, A000203.
%K nonn,changed
%O 1,2
%A _Robert G. Wilson v_
%E Offset corrected by _Donovan Johnson_, Jan 18 2012