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 A028972 Numbers represented by quadratic form with Gram matrix [ 7, 1, -3; 1, 3, 1; -3, 1, 7 ]. 0

%I

%S 0,3,7,8,12,15,20,23,27,28,32,35,40,43,47,48,52,55,60,63,67,68,72,75,

%T 80,83,87,88,92,95,103,107,108,112,115,120,123,127,128,132,135,140,

%U 143,147,148,152,155,160,163,167,168,172,175,180,183,187,188,192,195,200

%N Numbers represented by quadratic form with Gram matrix [ 7, 1, -3; 1, 3, 1; -3, 1, 7 ].

%p 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:

%K nonn

%O 1,2

%A _N. J. A. Sloane_.

%E More terms from _James A. Sellers_, May 31 2000

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Last modified July 28 09:26 EDT 2021. Contains 346323 sequences. (Running on oeis4.)