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%I #19 Feb 12 2021 04:50:51
%S 5,10,13,15,17,19,21,26,29,30,33,34,35,37,38,39,41,42,51,53,55,57,58,
%T 61,65,66,69,70,73,74,77,78,82,85,87,89,91,93,95,97,101,102,105,106,
%U 109,110,111,113,114,115,119,122,123,127,129,130,133,137,138,141,143
%N Squarefree numbers whose Euler totient function is not squarefree.
%C Numbers k such that abs(mu(k)) = 1 and mu(phi(k)) = 0.
%H Amiram Eldar, <a href="/A049197/b049197.txt">Table of n, a(n) for n = 1..10000</a>
%e 110 = 2*5*11 is squarefree but phi(110) = 40 is divisible by a square, so 110 is in the sequence.
%t Select[Range[144], SquareFreeQ[#] && !SquareFreeQ[EulerPhi[#]] &] (* _Amiram Eldar_, Feb 12 2021 *)
%o (PARI) isok(k) = issquarefree(k) && !issquarefree(eulerphi(k)); \\ _Michel Marcus_, Feb 12 2021
%Y Cf. A000010, A005117, A013929, A049195, A049196.
%K nonn
%O 1,1
%A _Labos Elemer_
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