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Numbers k such that phi(k) | sigma_8(k).
9

%I #20 Jan 08 2025 12:46:31

%S 1,2,3,6,19689,39378

%N Numbers k such that phi(k) | sigma_8(k).

%C sigma_8(n) is the sum of the 8th powers of the divisors of n.

%C sigma(16j+8,x)/phi(x) is an integer for j = 0, ..., 500 and 6 actual terms of this sequence. Compare to A015759, A015762, A015770 and A091285. - _Labos Elemer_, May 27 2004

%C No additional terms up to 5 million. - _Harvey P. Dale_, Jan 31 2016

%t Select[Range[40000],Divisible[DivisorSigma[8,#],EulerPhi[#]]&] (* _Harvey P. Dale_, Jan 31 2016 *)

%Y Cf. A015759, A015762, A015770, A091285.

%K nonn,more

%O 1,2

%A _Robert G. Wilson v_