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Numbers n such that sigma(n+1)=n+phi(n).
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%I #18 Aug 03 2014 14:37:22

%S 4,6,32,38,54,56,84,278,2664,10944,15608,20720,84800,179576,209664,

%T 6251904,85505600,125226624,584003328,19018936320,20534891040,

%U 79185129984,87065548800,191904215040,964494300024

%N Numbers n such that sigma(n+1)=n+phi(n).

%C Are there any odd values in the sequence?

%C a(26) > 10^12. - _Donovan Johnson_, Feb 29 2012

%t Select[Range[10^5], DivisorSigma[1, # + 1] == # + EulerPhi[#] &] (* _Alonso del Arte_, Feb 29 2012 *)

%o (PARI) : for(n=1,500000, if(sigma(n+1)-n==eulerphi(n),print1(n,",")))

%K easy,nonn

%O 1,1

%A _Benoit Cloitre_, Mar 02 2002

%E One more term from _Rick L. Shepherd_, Jun 21 2002

%E a(17)-a(25) from _Donovan Johnson_, Feb 29 2012