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%I #19 May 10 2022 11:17:13
%S 4,6,8,9,16,24,25,27,28,32,40,49,64,81,121,125,128,169,224,243,256,
%T 289,343,360,361,496,512,529,625,672,729,841,864,936,961,1024,1331,
%U 1369,1681,1849,2016,2048,2176,2187,2197,2209,2401,2809,3125,3481,3721,4096
%N Composite numbers k such that k/phi(k) - sigma(k)/k has numerator equal to 1.
%H Amiram Eldar, <a href="/A073540/b073540.txt">Table of n, a(n) for n = 1..10000</a>
%t Select[Range[4100], ! PrimeQ[#] && Numerator[#/EulerPhi[#] - DivisorSigma[1, #]/#] == 1 &] (* _Jayanta Basu_, Jul 01 2013 *)
%o (PARI) isok(k) = if (!isprime(k), numerator(k/eulerphi(k) - sigma(k)/k) == 1); \\ _Michel Marcus_, May 10 2022
%Y Cf. A000010, A000203, A017665, A017666, A076512, A109395.
%K easy,nonn
%O 1,1
%A _Benoit Cloitre_, Aug 27 2002