OFFSET
1,2
COMMENTS
If k belongs to the sequence, then sigma(3*k)/k is an integer, so sigma(3*k)/(3*k) is either an integer or a third of an integer, so 3*k is either multiperfect or belongs to A160320 or A160321. - Michel Marcus, Jul 09 2013
LINKS
Jud McCranie, Table of n, a(n) for n = 1..65
MATHEMATICA
k = 0; lst = {}; While[k < 10^11, If[ Mod[ DivisorSigma[1, 3 k], k] == 0, AppendTo[lst, k]]; k++]; lst (* Robert G. Wilson v, Mar 07 2021 *)
PROG
(PARI) isok(k) = !(sigma(3*k) % k); \\ Michel Marcus, Mar 07 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Alex Ratushnyak, Jul 05 2013
STATUS
approved