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%I #11 Apr 03 2023 10:36:11
%S 1,45,65,87,117,362,1053,1257,1282,1539,1798,2962,2966,3478,5002,5242,
%T 5932,9272,9374,9477,10550,10732,12975,13526,14427,20025,21782,21982,
%U 21986,22436,23386,23728,25978,25994,27764,32146,35306,35414,36412,38372,38675
%N Numbers n such that sigma(sigma(phi(n))) = sigma(sigma(n)).
%D M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards Applied Math. Series 55, 1964 (and various reprintings), p. 840.
%D T. M. Apostol, Introduction to Analytic Number Theory, Springer-Verlag, 1976, page 38
%H Donovan Johnson, <a href="/A172466/b172466.txt">Table of n, a(n) for n = 1..1000</a>
%H M. Abramowitz and I. A. Stegun, eds., <a href="http://www.convertit.com/Go/ConvertIt/Reference/AMS55.ASP">Handbook of Mathematical Functions</a>, National Bureau of Standards, Applied Math. Series 55, Tenth Printing, 1972 [alternative scanned copy].
%H C. K. Caldwell, The Prime Glossary, <a href="https://t5k.org/glossary/page.php?sort=SigmaFunction">sigma function</a>
%H K. Matthews, <a href="http://www.numbertheory.org/php/factor.html">Factorizing n and calculating phi(n),omega(n),d(n),sigma(n) and mu(n)</a>
%e phi(45) = 24; sigma(phi(45)) = sigma(24) = 60; sigma(sigma(phi(45))) = sigma(60) = 168; sigma(45) = 78; sigma(sigma(45)) = sigma(78) = 168.
%p with(numtheory): for n from 1 to 1000000 do; if sigma(sigma(phi(n)))= sigma(sigma(n)) then print(n);fi ; od;
%t Select[Range[40000],DivisorSigma[1,DivisorSigma[1,EulerPhi[#]]] == DivisorSigma[ 1, DivisorSigma[ 1,#]]&] (* _Harvey P. Dale_, Nov 22 2016 *)
%Y Cf. A001157, A001158, A001160, A001065.
%K nonn
%O 1,2
%A _Michel Lagneau_, Feb 03 2010