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 A243189 Nonnegative numbers of the form 2x^2 + 6xy - 3y^2. 2
 0, 2, 5, 8, 17, 18, 20, 32, 33, 42, 45, 50, 53, 68, 72, 77, 80, 98, 105, 113, 122, 125, 128, 132, 137, 153, 162, 168, 170, 173, 177, 180, 197, 200, 212, 213, 218, 233, 242, 245, 257, 258, 272, 288, 293, 297, 305, 308, 317, 320, 330, 338, 353, 357, 362, 378 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Discriminant 60. Nonnegative numbers of the form 5x^2 - 3y^2. - Jon E. Schoenfield, Jun 03 2022 From Klaus Purath, Jul 26 2023: (Start) Nonnegative integers k such that 3x^2 - 5y^2 + k = 0 has integer solutions. Also nonnegative integers of the form 2x^2 + (4m+2)xy + (2m^2+2m-7)y^2 for integers m. This includes the form in the name with m = 1. Also nonnegative integers of the form 5x^2 + 10mxy + (5m^2-3)y^2 for integers m. This includes the form from Jon E. Schoenfield above with m = 0. There are no squares in this sequence. Even powers of terms as well as products of an even number of terms belong to A243188. Odd powers of terms as well as products of an odd number of terms belong to the sequence. This can be proved with respect to the form 5x^2 - 3y^2 by the following identity: (na^2 - kb^2)(nc^2 - kd^2)(ne^2 - kf^2) = n[a(nce + kdf) + bk(cf + de)]^2 - k[na(cf + de) + b(nce + kdf)]^2 for all a, b, c, d, e, f, k, n in R. This can be verified by expanding both sides of the equation. (End) LINKS Table of n, a(n) for n=1..56. 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++, If[Reduce[2*x^2 + 6*x*y - 3*y^2 == n, {x, y}, Integers] =!= False, Sow[n]]]][[2, 1]] CROSSREFS Primes: A141303. Cf. A243188, A107152, A237606, A141302, A243190, A141304. Sequence in context: A240951 A280373 A324612 * A055236 A345430 A214124 Adjacent sequences: A243186 A243187 A243188 * A243190 A243191 A243192 KEYWORD nonn AUTHOR N. J. A. Sloane, Jun 05 2014 EXTENSIONS 0 prepended and more terms from Colin Barker, Apr 07 2015 STATUS approved

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Last modified September 22 11:05 EDT 2023. Contains 365520 sequences. (Running on oeis4.)