A068366 - OEIS

%I #15 Dec 11 2023 08:36:36

%S 1,7,15,127,267,315,495,621,969,1155,1917,5649,7515,12267,14911,17271,

%T 22347,26265,28671,30549,31641,32895,45195,48093,56697,60801,64923,

%U 77409,79827,82731,83559,116745,123387,172653,173901,179223,184869

%N Numbers k such that phi(sigma(k)+k) = sigma(k).

%C Are there any even values in the sequence?

%H Amiram Eldar, <a href="/A068366/b068366.txt">Table of n, a(n) for n = 1..1000</a>

%t q[n_] := Module[{s = DivisorSigma[1, n]}, EulerPhi[s + n] == s]; Select[Range[10^5], q] (* _Amiram Eldar_, Dec 11 2023 *)

%o (PARI) for(n=1,300000,if(eulerphi(sigma(n)+n)==sigma(n),print1(n,",")))

%Y Cf. A000010, A000203.

%K easy,nonn

%O 1,2

%A _Benoit Cloitre_, Feb 28 2002

%E More terms from _Rick L. Shepherd_, Apr 22 2002