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A028951 Numbers represented by quadratic form with Gram matrix [ 2, 1; 1, 4 ] (or the Kleinian 2-d lattice, see A002652). 6
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 (list; graph; refs; listen; history; text; internal format)
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
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
KEYWORD
nonn
AUTHOR
EXTENSIONS
More terms from Larry Reeves (larryr(AT)acm.org), Mar 29 2000
STATUS
approved

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Last modified May 20 12:18 EDT 2024. Contains 372712 sequences. (Running on oeis4.)