OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
Mod[sigma[3, a(n)], phi[a(n)]]=0; Mod[sigma[1, a(n)], phi[a(n)]]><0.
MATHEMATICA
Select[Range[1350], Divisible[DivisorSigma[3, #], (phi = EulerPhi[#])] && !Divisible[DivisorSigma[1, #], phi] &] (* Amiram Eldar, Jun 23 2019 *)
PROG
(PARI) isok(k) = my(phi=eulerphi(k)); ((sigma(k, 3) % phi) == 0) && (sigma(k) % phi); \\ Michel Marcus, Jun 23 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Dec 05 2002
STATUS
approved