OFFSET
1,2
COMMENTS
Discriminant 257.
16*a(n) has the form z^2 - 257*y^2, where z = 8*x+9*y. [Bruno Berselli, Jun 20 2014]
LINKS
R. J. Mathar, Table of n, a(n) for n = 1..2180
N. J. A. Sloane et al., Binary Quadratic Forms and OEIS (Index to related sequences, programs, references)
MATHEMATICA
maxTerm = 300; m0 = 10; dm = 10; Clear[f]; f[m_] := f[m] = Table[4*x^2 + 9 x*y - 11*y^2 , {x, -m, m}, {y, -m, m}] // Flatten // Union // Select[#, 0 <= # <= maxTerm&]&; f[m0]; f[m = m0]; While[f[m] != f[m - dm], m = m + dm]; f[m] (* Jean-François Alcover, Jun 04 2014 *) (* Brute force search, so not guaranteed to find all solutions, I believe. - N. J. A. Sloane, Jun 05 2014 *)
Reap[For[n = 0, n <= 30, n++,
If[Reduce[4*x^2 + 9*x*y - 11*y^2 == n, {x, y}, Integers] =!= False, Sow[n]]]][[2, 1]] (* Better program, not brute force, but slow. Confirms the terms up through 29. - N. J. A. Sloane, Jun 05 2014 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jun 02 2014
STATUS
approved