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%I #17 Sep 12 2014 16:07:27
%S 23,51,77,87,114,154,158,184,210,308,552,690,786,1330,1848,2030,2280,
%T 2868,2976,3432,8680,10290,11556,12750,13110,26400,56808,57960,62496,
%U 136290,170478,608580
%N Numbers n such that sigma(n) = phi(prime(n)+1).
%C The sequence may be finite. Typically phi(prime(n)+1) will be on the order of n*log(n), while according to Grönwall's theorem sigma(n) = O(n * log log(n)). - _Robert Israel_, Sep 12 2014
%p with(numtheory): A067625:=n->`if`(sigma(n)=phi(ithprime(n)+1),n,NULL): seq(A067625(n),n=1..10^5); # _Wesley Ivan Hurt_, Sep 12 2014
%t Select[Range[610000],DivisorSigma[1,#]==EulerPhi[Prime[#]+1]&] (* _Harvey P. Dale_, Mar 17 2012 *)
%o (PARI) a067625(m) = for(n=1,m, if(sigma(n)==eulerphi(prime(n)+1),print1(n,",")))
%K nonn
%O 1,1
%A _Benoit Cloitre_, Feb 23 2002
%E More terms from _Klaus Brockhaus_, Mar 02 2002