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 A211148 Number of 2 X 2 matrices having all terms in {-n,...,0,..,n} and positive determinant. 3
 24, 248, 1056, 3008, 6904, 13624, 24448, 40576, 63640, 95288, 137632, 192384, 262392, 349688, 457088, 587520, 744344, 930104, 1149152, 1404160, 1699640, 2039544, 2428352, 2869312, 3368472, 3929912, 4558688, 5259712, 6039480 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS For a guide to related sequences, see A210000. LINKS MATHEMATICA 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] Table[c[n, 0], {n, 1, z1}]   (* A209981 *) c1[n_, m_] := c1[n, m] = Sum[c[n, k], {k, 1, m}] t = Table[c1[n, 2*n^2], {n, 1, z1}]   (* A211148 *) 2 t   (* A211149 *) t/8   (* integers *) CROSSREFS Cf. A210000. Sequence in context: A267060 A086603 A281076 * A265858 A282859 A000594 Adjacent sequences:  A211145 A211146 A211147 * A211149 A211150 A211151 KEYWORD nonn AUTHOR Clark Kimberling, Apr 04 2012 STATUS approved

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Last modified July 26 18:35 EDT 2017. Contains 289839 sequences.