OFFSET
1,1
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..1000
MATHEMATICA
Select[Range[1000], Mod[#, 3] > 0 && Divisible[DivisorSigma[1, #], EulerPhi[#+4]] &] (* Amiram Eldar, Dec 13 2018 *)
PROG
(PARI) is(n)=n%3 && !(sigma(n)%eulerphi(n+4)) \\ Charles R Greathouse IV, Sep 25 2012
(Magma) [n: n in [1..1000] | n mod 3 ne 0 and DivisorSigma(1, n) mod EulerPhi(n+4) eq 0]; // G. C. Greubel, Dec 13 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
Title and PARI program corrected by Sean A. Irvine, Dec 13 2018
STATUS
approved