OFFSET
1,2
COMMENTS
Odd terms of A202822, which lists Löschian numbers of the form 3*k+1. - Altug Alkan, Nov 15 2015
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
Joerg Arndt, Plane-filling curves on all uniform grids, arXiv preprint arXiv:1607.02433 [math.CO], 2016.
MATHEMATICA
nn = 25; Select[Union[Flatten[Table[x^2 + x*y + y^2, {x, 0, nn}, {y, 0, x}]]], Mod[#, 6] == 1 && # <= nn^2&] (* Jean-François Alcover, Jul 21 2018, after T. D. Noe *)
PROG
(PARI) is(n)=(n%6==1)&&#bnfisintnorm(bnfinit(z^2+z+1), n);
select(n->is(n), vector(500, j, j))
(PARI) x='x+O('x^500); p=eta(x)^3/eta(x^3); for(n=0, 499, if(polcoeff(p, n) != 0 && n%6==1, print1(n, ", "))) \\ Altug Alkan, Nov 15 2015
(PARI) isok(n) = if( n<1 || (n%3 == 0), 0, 0 != sumdiv( n, d, kronecker( -3, d))) && n%2==1;
for(n=0, 500, if(isok(n), print1(n", "))) \\ Altug Alkan, Nov 15 2015
(PARI) list(lim)=my(v=List(), y, t); for(x=0, sqrtint(lim\3), my(y=x, t); while((t=x^2+x*y+y^2)<=lim, if(t%6==1, listput(v, t)); y++)); Set(v) \\ Charles R Greathouse IV, Jul 05 2017
(Haskell)
a260682 n = a260682_list !! (n-1)
a260682_list = filter ((== 1) . flip mod 6) a003136_list
-- Reinhard Zumkeller, Nov 16 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
Joerg Arndt, Nov 15 2015
STATUS
approved