%I #18 Apr 17 2022 21:15:23
%S 2318,2806,5734,5937,7198,8097,10126,11295,11818,13054,17324,20374,
%T 21838,22947,27694,29145,32086,33826,35074,38997,42334,42458,43798,
%U 46726,54825,56974,58438,61366,66202,68686,71614,86762,86924,87435
%N Numbers n such that sigma(2*phi(n)) = 2*sigma(n).
%H Charles R Greathouse IV, <a href="/A137733/b137733.txt">Table of n, a(n) for n = 1..10000</a>
%H Jean-Marie De Koninck and Florian Luca, <a href="http://www.cs.uwaterloo.ca/journals/JIS/VOL11/DeKoninck/dekoninck47.html">Positive integers n such that sigma(phi(n)) = sigma(n)</a>, Journal of Integer Sequences, Paper No. 08.1.5, 2008.
%e a(1) = 2318, because this is the smallest integer such that sigma(2*phi(n)) = 2*sigma(n).
%t Select[Range[90000],DivisorSigma[1,2*EulerPhi[#]]==2*DivisorSigma[1,#]&] (* _Harvey P. Dale_, Jan 31 2015 *)
%o (PARI) is(n)=sigma(2*eulerphi(n))==2*sigma(n) \\ _Charles R Greathouse IV_, Feb 04 2013
%K nonn
%O 1,1
%A _Jeffrey Shallit_, Feb 09 2008; definition corrected Feb 09 2008