A243191 Nonnegative integers represented by the indefinite quadratic form x^2+7xy-y^2.

0, 1, 4, 7, 9, 11, 13, 16, 17, 25, 28, 29, 36, 37, 43, 44, 47, 49, 52, 53, 59, 63, 64, 68, 77, 81, 89, 91, 97, 99, 100, 107, 112, 113, 116, 117, 119, 121, 131, 143, 144, 148, 149, 153, 163, 169, 172, 175, 176, 187, 188, 196, 197, 199, 203, 208, 211, 212, 221

Offset: 1

Author

N. J. A. Sloane, Jun 06 2014

Keywords

• nonn

Comments

Discriminant 53.

Same as nonnegative integers represented by the form x^2 - 53*y^2 (or 53*x^2 - y^2). - Robert Israel, Jun 11 2014

Links

• Robert Israel, Table of n, a(n) for n = 1..10000
• N. J. A. Sloane et al., Binary Quadratic Forms and OEIS (Index to related sequences, programs, references)

Crossrefs

Cf. A141189 (primes of the form x^2+7*x*y-y^2).

Programs

Maple

select(t -> nops([isolve(x^2-53*y^2=t)])>0, [$0..1000]); # Robert Israel, Jun 11 2014

Mathematica

Reap[For[n = 0, n <= 30, n++, If[Reduce[1*x^2 + 7*x*y - 1*y^2 == n, {x, y}, Integers] =!= False, Sow[n]]]][[2, 1]]

Extensions

More terms from Colin Barker, Jun 10 2014