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A028972 Numbers represented by quadratic form with Gram matrix [ 7, 1, -3; 1, 3, 1; -3, 1, 7 ]. 0
0, 3, 7, 8, 12, 15, 20, 23, 27, 28, 32, 35, 40, 43, 47, 48, 52, 55, 60, 63, 67, 68, 72, 75, 80, 83, 87, 88, 92, 95, 103, 107, 108, 112, 115, 120, 123, 127, 128, 132, 135, 140, 143, 147, 148, 152, 155, 160, 163, 167, 168, 172, 175, 180, 183, 187, 188, 192, 195, 200 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..60.

MAPLE

L := [seq(0, i=1..1)]: for x from -20 to 20 do for y from -20 to 20 do for z from -20 to 20 do if member(7*x^2+2*x*y-6*x*z+3*y^2+2*y*z+7*z^2, L)=false then L := [op(L), 7*x^2 +2*x*y-6*x*z+3*y^2+2*y*z+7*z^2] fi: od: od: od: L2 := sort(L): for i from 1 to 100 do printf(`%d, `, L2[i]) od:

CROSSREFS

Sequence in context: A007970 A255342 A134258 * A153030 A031425 A063657

Adjacent sequences:  A028969 A028970 A028971 * A028973 A028974 A028975

KEYWORD

nonn

AUTHOR

N. J. A. Sloane.

EXTENSIONS

More terms from James A. Sellers, May 31 2000

STATUS

approved

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Last modified February 20 18:41 EST 2018. Contains 299381 sequences. (Running on oeis4.)