A028951 Numbers represented by quadratic form with Gram matrix [ 2, 1; 1, 4 ] (or the Kleinian 2-d lattice, see A002652).

0, 1, 2, 4, 7, 8, 9, 11, 14, 16, 18, 22, 23, 25, 28, 29, 32, 36, 37, 43, 44, 46, 49, 50, 53, 56, 58, 63, 64, 67, 71, 72, 74, 77, 79, 81, 86, 88, 92, 98, 99, 100, 106, 107, 109, 112, 113, 116, 121, 126, 127, 128, 134, 137, 142, 144, 148, 149, 151, 154, 158, 161, 162

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn

Comments

Or, numbers of the form x^2+xy+2y^2 with x and y integers. - N. J. A. Sloane, Apr 30 2015

Links

• N. J. A. Sloane et al., Binary Quadratic Forms and OEIS (Index to related sequences, programs, references)

Crossrefs

Cf. A028929, A035248, A002652, A034036, A257346 (complement).

Programs

Mathematica

Reap[For[n = 0, n < 200, n++, r = Reduce[x^2 + x y + 2 y^2 == n, {x, y}, Integers]; If[r =!= False, Sow[n]]]][[2, 1]] (* Jean-François Alcover, Oct 31 2016 *)

Extensions

More terms from Larry Reeves (larryr(AT)acm.org), Mar 29 2000