OFFSET
1,1
COMMENTS
Includes primes p such that (p+9)/8 is prime. Thus Dickson's conjecture implies the sequence is infinite. - Robert Israel, Jan 10 2019
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
MAPLE
select(n -> (numtheory:-sigma(n)/numtheory:-phi(n+9))::integer, [seq(seq(3*i+j, j=1..2), i=0..1000)]); # Robert Israel, Jan 10 2019
MATHEMATICA
Select[Range[1, 5000], Divisible[DivisorSigma[1, #], EulerPhi[9 + #]] && ! Mod[#, 3] == 0 &] (* David Nacin, Mar 04 2012 *)
PROG
(PARI) is(n)=n%3 && sigma(n)%eulerphi(n+9)==0 \\ Charles R Greathouse IV, Sep 25 2012
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved