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 A211059 Number of 2 X 2 matrices having all terms in {1,...,n} and positive determinant. 3
 0, 5, 33, 112, 288, 605, 1145, 1968, 3176, 4861, 7161, 10152, 14040, 18917, 24961, 32352, 41312, 51949, 64585, 79320, 96472, 116277, 139025, 164840, 194184, 227261, 264385, 305840, 352096, 403245, 459945, 522312, 590840, 665917 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS For a guide to related sequences, see A210000. LINKS MATHEMATICA a = 1; b = n; z1 = 35; 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, n^2] - c[n, 0], {n, 1, z1}]   (* A211059 *) 2*%     (* A211056 *) CROSSREFS Cf. A210000, A211056. Sequence in context: A250225 A250273 A050830 * A146263 A255943 A270222 Adjacent sequences:  A211056 A211057 A211058 * A211060 A211061 A211062 KEYWORD nonn AUTHOR Clark Kimberling, Mar 31 2012 STATUS approved

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