%I #16 Sep 08 2022 08:44:40

%S 7,21,32,46,60,77,123,124,132,221,224,254,261,287,308,312,376,437,445,

%T 506,534,539,665,680,717,752,770,798,860,948,1239,1264,1340,1517,1519,

%U 1617,1628,1815,2021,2275,2288,2320,2379,2400,2871,2890

%N Numbers n such that phi(n) * sigma(n) + 16 is a perfect square.

%H Harvey P. Dale, <a href="/A015729/b015729.txt">Table of n, a(n) for n = 1..500</a>

%H Richard K. Guy, <a href="http://www.jstor.org/stable/2974586">Divisors and desires</a>, Amer. Math. Monthly, 104 (1997), 359-360.

%t Select[Range[3000],IntegerQ[Sqrt[EulerPhi[#]DivisorSigma[1,#]+16]]&] (* _Harvey P. Dale_, Dec 07 2012 *)

%o (Magma) [n: n in [1..3000] | IsSquare(EulerPhi(n) * SumOfDivisors(n)+16)]; // _Vincenzo Librandi_, Mar 14 2014

%K nonn

%O 1,1

%A _Robert G. Wilson v_