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A209994
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Number of 2x2 matrices with all elements in {1,2,...,n} and determinant in {-1,0,1}.
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1
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0, 1, 10, 31, 60, 105, 154, 223, 300, 393, 490, 607, 748, 889, 1034, 1215, 1404, 1593, 1818, 2031, 2300, 2569, 2810, 3071, 3436, 3753, 4042, 4399, 4796, 5129, 5610, 5967, 6412, 6857, 7242, 7759, 8380, 8809, 9242, 9775, 10460
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OFFSET
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0,3
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COMMENTS
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See A210000 for a guide to related sequences.
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LINKS
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Table of n, a(n) for n=0..40.
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MATHEMATICA
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a = 1; b = n; z1 = 40;
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, -m, m}]
Table[c1[n, 1], {n, 0, z1}] (* A209994 *)
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CROSSREFS
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Cf. A210000.
Sequence in context: A187633 A063154 A100500 * A211013 A085473 A051943
Adjacent sequences: A209991 A209992 A209993 * A209995 A209996 A209997
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KEYWORD
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nonn
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AUTHOR
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Clark Kimberling, Mar 18 2012
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STATUS
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approved
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