A077449 - OEIS

%I #17 Sep 08 2020 05:50:49

%S 3,6,15,30,31,39,43,51,57,62,67,71,75,78,79,86,87,102,103,111,114,123,

%T 131,134,139,142,147,150,155,158,159,174,183,191,195,206,215,219,222,

%U 223,239,246,255,262,267,278,279,283,285,291,294,303,310,311,318,327

%N Numbers k such that Sum_{d|k} mu(phi(d)) = 0.

%H Amiram Eldar, <a href="/A077449/b077449.txt">Table of n, a(n) for n = 1..10000</a>

%H Vaclav Kotesovec, <a href="/A077449/a077449.jpg">Plot of a(n)/n for n = 1..360000</a>

%F a(n) seems to be asymptotic to c*n where c is around 5.47...

%t Select[Range[400],Total[MoebiusMu[EulerPhi[#]]&/@Divisors[#]]==0&] (* _Harvey P. Dale_, Dec 22 2018 *)

%t Select[Range[330], DivisorSum[#, MoebiusMu[EulerPhi[#1]] &] == 0 &] (* _Amiram Eldar_, Sep 08 2020 *)

%o (PARI) isok(k) = sumdiv(k, d, moebius(eulerphi(d))) == 0; \\ _Michel Marcus_, Sep 08 2020

%Y Cf. A000010, A008683.

%K nonn

%O 1,1

%A _Benoit Cloitre_, Nov 30 2002