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A043293 Numbers n such that lcm(sigma(n),phi(n)) is a perfect square. 1


%S 1,3,10,17,70,170,210,357,364,416,456,577,679,1092,1154,1358,1672,

%T 1705,1820,2280,2387,2565,2652,2835,2885,2910,3395,3570,4212,4577,

%U 4774,4947,5016,5044,5115,5130,5412,5670,5770,5863,6188,6790,7072,7161,7471,7546

%N Numbers n such that lcm(sigma(n),phi(n)) is a perfect square.

%C If n is in the sequence and n>10 LCM(sigma(n),phi(n))==0 (mod 6)

%H Amiram Eldar, <a href="/A043293/b043293.txt">Table of n, a(n) for n = 1..10000</a>

%F n such that sqrt(A009286(n))=floor(sqrt(A009286(n)))

%t Select[Range[8000], IntegerQ @ Sqrt @ LCM[EulerPhi[#], DivisorSigma[1, #]] &] (* _Amiram Eldar_, Aug 12 2019 *)

%Y Cf. A009286.

%K nonn

%O 1,2

%A _Benoit Cloitre_, Apr 04 2002

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Last modified December 7 20:40 EST 2021. Contains 349589 sequences. (Running on oeis4.)