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 A211152 Number of 2 X 2 matrices having all terms in {-n,...,0,...,n} and determinant >= 2n. 2
 4, 80, 428, 1428, 3604, 7924, 14988, 26244, 43072, 66844, 98804, 142652, 197584, 268800, 357608, 465888, 596964, 756036, 942160, 1163608, 1420248, 1717344, 2056952, 2451248, 2891420, 3392528, 3958576 (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 = 27; 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, -2*n^2, m}] Table[c1[n, 2*n^2]-c1[n, 2n-1], {n, 1, z1}] (* A211152 *) %/4 (* integers *) CROSSREFS Cf. A210000. Sequence in context: A125710 A204296 A192790 * A093854 A345459 A269146 Adjacent sequences: A211149 A211150 A211151 * A211153 A211154 A211155 KEYWORD nonn AUTHOR Clark Kimberling, Apr 05 2012 STATUS approved

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Last modified March 25 07:51 EDT 2023. Contains 361511 sequences. (Running on oeis4.)