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 A028958 Numbers represented by quadratic form with Gram matrix [ 2, 1; 1, 12 ] (divided by 2). 4
 0, 1, 4, 6, 8, 9, 12, 16, 18, 23, 24, 25, 26, 27, 32, 36, 39, 48, 49, 52, 54, 58, 59, 62, 64, 72, 78, 81, 82, 87, 92, 93, 94, 96, 100, 101, 104, 108, 116, 117, 121, 123, 124, 128, 138, 141, 142, 144, 146, 150, 156, 162, 164, 167, 169, 173, 174, 184, 186, 188, 192 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Nonnegative integers of the form x^2 + x*y + 6*y^2, discriminant -23. - Ray Chandler, Jul 12 2014 The Gram matrix is positive-definite, therefore, if w := (1 + sqrt(-23)) / 2, then |x + w*y|^2 = x^2 + x*y + 6*y^2 > 0 for all integers x and y except x = y = 0. - Michael Somos, Mar 28 2015 The theta function of the lattice with basis [1, w] is the g.f. of A028959, therefore, A028959(n) is positive if and only if n is in this sequence. - Michael Somos, Mar 28 2015 LINKS N. J. A. Sloane et al., Binary Quadratic Forms and OEIS (Index to related sequences, programs, references) CROSSREFS For primes see A033217. Cf. A028929, A106867. Cf. A028959. Sequence in context: A062002 A090419 A209799 * A200878 A344030 A036310 Adjacent sequences:  A028955 A028956 A028957 * A028959 A028960 A028961 KEYWORD nonn AUTHOR EXTENSIONS More terms from Larry Reeves (larryr(AT)acm.org), Mar 29 2000 STATUS approved

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Last modified September 23 14:40 EDT 2021. Contains 347618 sequences. (Running on oeis4.)