A043293 - OEIS

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

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

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

FORMULA

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

MATHEMATICA

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

CROSSREFS