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 A242663 Nonnegative integers of the form x^2 + 4*x*y - 4*y^2. 4
 0, 1, 4, 8, 9, 16, 17, 25, 28, 32, 36, 41, 49, 56, 64, 68, 72, 73, 81, 89, 92, 97, 100, 112, 113, 121, 124, 128, 136, 137, 144, 153, 161, 164, 169, 184, 188, 193, 196, 200, 217, 224, 225, 233, 241, 248, 252, 256, 257, 272, 281, 284, 288, 289, 292 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Discriminant 32. Also numbers representable as x^2 + 6*x*y + y^2 with 0 <= x <= y. - Gheorghe Coserea, Jul 29 2018 Also numbers of the form x^2 - 8*y^2. - Jianing Song, Jul 31 2018 LINKS Gheorghe Coserea, Table of n, a(n) for n = 1..100001 N. J. A. Sloane et al., Binary Quadratic Forms and OEIS (Index to related sequences, programs, references) MATHEMATICA Reap[For[n = 0, n <= 300, n++, If[Reduce[ x^2 + 4*x*y - 4*y^2 == n, {x, y}, Integers] =!= False, Sow[n]]]][[2, 1]] PROG (PARI) seq(M, k=6) = { setintersect([1..M], setbinop((x, y)->x^2 + k*x*y + y^2, [0..1+sqrtint(M)])); }; concat(0, seq(292)) \\ Gheorghe Coserea, Jul 31 2018 CROSSREFS Cf. A031363. Primes in this sequence = A007519. Sequence in context: A237882 A153034 A106840 * A160053 A140612 A225353 Adjacent sequences:  A242660 A242661 A242662 * A242664 A242665 A242666 KEYWORD nonn AUTHOR N. J. A. Sloane, May 31 2014 STATUS approved

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Last modified May 17 19:26 EDT 2021. Contains 343988 sequences. (Running on oeis4.)