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

1, 3, 10, 17, 70, 170, 210, 357, 364, 416, 456, 577, 679, 1092, 1154, 1358, 1672, 1705, 1820, 2280, 2387, 2565, 2652, 2835, 2885, 2910, 3395, 3570, 4212, 4577, 4774, 4947, 5016, 5044, 5115, 5130, 5412, 5670, 5770, 5863, 6188, 6790, 7072, 7161, 7471, 7546

Offset: 1

Author

Benoit Cloitre, Apr 04 2002

Keywords

• nonn

Comments

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

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A009286.

Programs

Mathematica

Select[Range[8000], IntegerQ @ Sqrt @ LCM[EulerPhi[#], DivisorSigma[1, #]] &] (* Amiram Eldar, Aug 12 2019 *)

Formula

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