OFFSET
1,1
COMMENTS
A000086(a(n)) = 0.
Also numbers n with psi(n) congruent to 0 mod 3, where psi is A001615, and also numbers divisible by 9 or by at least one prime of the form 3k-1: A003627. - Enrique Pérez Herrero, Dec 08 2013
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
MATHEMATICA
Select[Range[1000], Mod[# * Times@@(1+1/Transpose[FactorInteger[#]][[1]]), 3]==0&] (* Enrique Pérez Herrero, Dec 08 2013 *)
nn = 10; lim = 1 + nn + nn^2; Complement[Range[2, lim], Select[Union[Flatten[Table[If[GCD[x, y] == 1, x^2 + x*y + y^2, 0], {y, nn}, {x, y}]]], # <= lim &]] (* T. D. Noe, Dec 09 2013 *)
PROG
(Haskell)
a226946 n = a226946_list !! (n-1)
a226946_list = filter ((== 0) . a000086) [1..]
-- Reinhard Zumkeller, Dec 16 2013, Jun 23 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Jun 23 2013
EXTENSIONS
The original definition was too weak; thanks to T. D. Noe for having corrected this. - Reinhard Zumkeller, Dec 09 2013
STATUS
approved