OFFSET
1,1
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..210
Richard K. Guy, Divisors and desires, Amer. Math. Monthly, 104 (1997), 359-360.
MATHEMATICA
Select[Range[10000], IntegerQ[Sqrt[EulerPhi[#]DivisorSigma[1, #] + 9]] &] (* Vincenzo Librandi, Mar 14 2014 *)
PROG
(Magma) [n: n in [1..6000] | IsSquare(EulerPhi(n) * SumOfDivisors(n) + 9)]; // Vincenzo Librandi, Mar 14 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved