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A135658 Nonprimes of the form 4x^2-4xy+7y^2. 0
4, 15, 16, 24, 28, 36, 40, 55, 60, 63, 64, 87, 88, 96, 100, 112, 124, 132, 135, 144, 159, 160, 168, 175, 196, 216, 220, 231, 232, 240, 247 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Because 4x^2-4*x*y+7*y^2 = (2*x-y)^2+6*y^2, this is a subsequence of A002481. - R. J. Mathar, Jan 18 2021

LINKS

Table of n, a(n) for n=1..31.

MATHEMATICA

Do[Do[w = 4x^2 - 4x y + 7y^2; If[w > 0, If[PrimeQ[w], [null], AppendTo[a, w]]], {x, 0, 100}], {y, 0, 100}]; Union[a]

CROSSREFS

Cf. A107006, A124477, A135657.

Sequence in context: A260577 A152442 A161769 * A228589 A066862 A228590

Adjacent sequences:  A135655 A135656 A135657 * A135659 A135660 A135661

KEYWORD

nonn

AUTHOR

Artur Jasinski, Nov 25 2007

STATUS

approved

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Last modified September 25 15:27 EDT 2021. Contains 347658 sequences. (Running on oeis4.)