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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
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
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
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, May 31 2014
STATUS
approved