OFFSET
1,2
COMMENTS
Numbers k such that Ramanujan tau(k), A000594(k), is not a multiple of 3.
Not a multiplicative semigroup. For example, although 7 is included, 49 = 7*7 is not.
LINKS
MATHEMATICA
Select[Range[380], Mod[#, 3]!=0&&Mod[DivisorSigma[1, #], 3]!=0 &] (* Stefano Spezia, Jul 03 2024 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Antti Karttunen, Jul 03 2024
STATUS
approved