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A243705 Nonnegative numbers represented by the indefinite quadratic form 3x^2+13xy-3y^2. 1
0, 3, 7, 12, 13, 15, 17, 27, 28, 35, 47, 48, 52, 53, 60, 63, 65, 67, 68, 75, 85, 93, 97, 108, 112, 117, 123, 135, 137, 140, 147, 153, 157, 167, 175, 177, 183, 188, 192, 193, 208, 212, 217, 227, 233, 235, 240, 243, 252, 257, 260, 263, 265, 268 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Discriminant 205.

12*a(n) has the form z^2 - 205*y^2, where z = 6*x+13*y. In fact, this is a particular case of the following identity on the numbers of the form a*x^2+b*x*y+c*y^2: 4*a*(a*x^2+b*x*y+c*y^2) = (2*a*x+b*y)^2-(b^2 -4*a*c)*y^2. [Bruno Berselli, Jun 20 2014]

LINKS

Table of n, a(n) for n=1..54.

Will Jagy, C++ program Conway_Positive_All.cc to find all positive numbers represented by an indefinite binary quadratic form

Will Jagy, Sample output from Conway_Positive_All.cc

N. J. A. Sloane et al., Binary Quadratic Forms and OEIS (Index to related sequences, programs, references)

PROG

(C++, Jagy's program, see link)

Conway_Positive_All 3 13 -3 500

CROSSREFS

Primes: A243706.

Sequence in context: A332464 A256563 A349888 * A057927 A298788 A056772

Adjacent sequences:  A243702 A243703 A243704 * A243706 A243707 A243708

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Jun 17 2014

STATUS

approved

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Last modified September 24 15:00 EDT 2022. Contains 356936 sequences. (Running on oeis4.)