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Squarefree numbers whose Euler totient function is also squarefree.
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%I #17 Sep 08 2022 08:44:58

%S 1,2,3,6,7,11,14,22,23,31,43,46,47,59,62,67,71,79,83,86,94,103,107,

%T 118,131,134,139,142,158,166,167,179,191,206,211,214,223,227,239,262,

%U 263,278,283,311,331,334,347,358,359,367,382,383,419,422,431,439,443,446

%N Squarefree numbers whose Euler totient function is also squarefree.

%H Amiram Eldar, <a href="/A049196/b049196.txt">Table of n, a(n) for n = 1..10000</a>

%F k such that abs(mu(k)) = 1 and abs(mu(phi(k))) = 1.

%e 86 is here because it is squarefree and the same holds for phi(86) = 42.

%t Select[Range[500],And@@SquareFreeQ/@{#,EulerPhi[#]}&] (* _Harvey P. Dale_, Nov 05 2013 *)

%o (Magma) [n:n in [1..500]| IsSquarefree(n) and IsSquarefree(EulerPhi(n))]; // _Marius A. Burtea_, Jul 11 2019

%o (PARI) isok(m) = issquarefree(m) && issquarefree(eulerphi(m)); \\ _Michel Marcus_, Jul 12 2019

%Y A000010, A005117, A013929.

%K nonn

%O 1,2

%A _Labos Elemer_