# Greetings from The On-Line Encyclopedia of Integer Sequences! http://oeis.org/

Search: id:a097652
Showing 1-1 of 1

%I A097652 #16 May 07 2024 07:04:41
%S A097652 1,2,20,48,180,208,864,1120,1368,3552,58320,76416,79968,95488,107520,
%T A097652 338688,570240,595968,653184,1347840,5199552,7918848,14592000,
%U A097652 93699072,159138176,167078784,246688000,281640960,314548224,323985408,338411520,347578368,352002048
%N A097652 Numbers n such that n=phi(phi(n)+sigma(n)) and n is not of the form 2*p where p is a Sophie Germain odd prime.
%C A097652 It is obvious that if n=2*p where p is a Sophie Germain odd prime then n=phi(phi(n)+sigma(n)). This sequence is a subsequence of A097646. Except for the first term all terms of this sequence are even. There is no other term up to 3*10^7.
%H A097652 C. K. Caldwell, The Prime Glossary, <a href="https://t5k.org/glossary/page.php?sort=SophieGermainPrime">Sophie Germain prime</a>.
%e A097652 14592000 is in the sequence because 14592000=2*7296000, 7296000 is not a Sophie Germain odd prime and phi(phi(14592000)+sigma(14592000)) =14592000.
%t A097652 Do[If[(!PrimeQ[n/2]||!PrimeQ[n+1])&&n==EulerPhi[EulerPhi[n]+ DivisorSigma[1, n]], Print[n]], {n, 30000000}]
%Y A097652 Cf. A097646, A005384.
%K A097652 nonn
%O A097652 1,2
%A A097652 _Farideh Firoozbakht_, Sep 09 2004
%E A097652 a(24)-a(33) from _Donovan Johnson_, Jan 18 2012

# Content is available under The OEIS End-User License Agreement: http://oeis.org/LICENSE