A028951 - OEIS

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

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OFFSET

1,3

COMMENTS

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

LINKS

Table of n, a(n) for n=1..63.

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

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 *)

CROSSREFS

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

Sequence in context: A047351 A242937 A247979 * A035248 A190244 A182636

Adjacent sequences: A028948 A028949 A028950 * A028952 A028953 A028954

KEYWORD

nonn

AUTHOR

N. J. A. Sloane.

EXTENSIONS

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

STATUS

approved