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 A209994 Number of 2x2 matrices with all elements in {1,2,...,n} and determinant in {-1,0,1}. 1
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS See A210000 for a guide to related sequences. LINKS MATHEMATICA 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 *) CROSSREFS Cf. A210000. Sequence in context: A187633 A063154 A100500 * A211013 A085473 A051943 Adjacent sequences:  A209991 A209992 A209993 * A209995 A209996 A209997 KEYWORD nonn AUTHOR Clark Kimberling, Mar 18 2012 STATUS approved

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