%I #22 May 09 2022 08:36:19
%S 5225,20405,181685,210395,302375,302445,524975,1469555,1563485,
%T 1748855,2791085,3097055,4418375,4542065,4735115,5482235,5567705,
%U 5568615,5683205,5753405,6457055,7363013,7531205,8016435,8043875,9534185,10511345,10790325,11504405
%N Numbers k such that phi(5k-1) = sigma(k).
%C Are there any terms not congruent to 5 in the sequence?
%C a(22) = 7363013 is the first example. - _Charles R Greathouse IV_, Jan 29 2012
%t Select[Range[10^6], EulerPhi[5*# - 1] == DivisorSigma[1, #] &] (* _Amiram Eldar_, May 09 2022 *)
%o (PARI) for(n=1,1e8,if(sigma(n)==eulerphi(5*n-1),print1(n", "))) \\ _Charles R Greathouse IV_, Jan 29 2012
%Y Cf. A000010, A000203, A067226, A067235.
%K nonn
%O 1,1
%A _Benoit Cloitre_, Feb 20 2002
%E a(8)-a(29) from _Donovan Johnson_, Jan 29 2012