OFFSET
1,2
COMMENTS
sigma_3(k) is the sum of the cubes of the divisors of k (A001158).
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
MATHEMATICA
Select[Range[630], Divisible[DivisorSigma[3, #], EulerPhi[#]] &] (* Amiram Eldar, Jun 23 2019 *)
PROG
(PARI) isok(k) = (sigma(k, 3) % eulerphi(k)) == 0; \\ Michel Marcus, Jun 23 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved