OFFSET
1,1
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
EXAMPLE
MATHEMATICA
amax = 2000; xmax = Sqrt[amax] // Ceiling; Clear[f]; f[_] = 0; Do[q = x^2 + x y + y^2; f[q] = f[q] + 1, {x, 0, xmax}, {y, x, xmax}];
A198773 = Select[Range[0, 3 xmax^2], # <= amax && f[#] == 2&] (* Jean-François Alcover, Jun 21 2018 *)
PROG
(Haskell)
a198773 n = a198773_list !! (n-1)
a198773_list = filter ((== 2) . a088534) a003136_list
(PARI) is(n)=my(t=#bnfisintnorm(bnfinit(z^2+z+1), n)); t==3 || t==4;
select(n->is(n), vector(1500, j, j)) \\ Joerg Arndt, Jan 11 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Oct 30 2011
STATUS
approved