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A211147
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Number of 2 X 2 matrices having all terms in {-n,...,0,...,n} and nonnegative determinant.
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1
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1, 57, 377, 1345, 3553, 7737, 14937, 26177, 42945, 66681, 99193, 142209, 198241, 269049, 357593, 466433, 598401, 756281, 944057, 1164289, 1421601, 1719161, 2061081, 2451329, 2895489, 3396729, 3960569, 4591937, 5296289, 6077881
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OFFSET
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0,2
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COMMENTS
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It appears that all terms are of the form 8*k + 1.
For a guide to related sequences, see A210000.
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LINKS
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MATHEMATICA
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a = -n; b = n; z1 = 30;
t[n_] := t[n] = Flatten[Table[w*z - x*y, {w, a, b}, {x, a, b}, {y, a, b}, {z, a, b}]]
c[n_, k_] := c[n, k] = Count[t[n], k]
c1[n_, m_] := c1[n, m] = Sum[c[n, k], {k, 0, m}]
Table[c1[n, 2 n^2], {n, 0, z1}]
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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