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 A211157 Number of 2 X 2 matrices having all terms in {-n,...,0,..,n} and positive even determinant. 4
 4, 164, 528, 1968, 3844, 8836, 14144, 26176, 37540, 61188, 82192, 123120, 157924, 223268, 276608, 374272, 452420, 591524, 700752, 891760, 1038980, 1293700, 1487744, 1818112, 2067172 (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 = 25; 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] u[n_] := u[n] = Sum[c[n, 2 k], {k, 0, 2*n^2}] v[n_] := v[n] = Sum[c[n, 2 k], {k, 1, 2*n^2}] w[n_] := w[n] = Sum[c[n, 2 k - 1], {k, 1, 2*n^2}] u1 = Table[u[n], {n, 1, z1}] (* A211156 *) v1 = Table[v[n], {n, 1, z1}] (* A211157 *) w1 = Table[w[n], {n, 1, z1}] (* A211158 *) (u1 - 1)/4 (* integers *) v1/4 (* integers *) w1/4 (* integers *) CROSSREFS Cf. A210000. Sequence in context: A306350 A125532 A229405 * A185857 A221654 A159011 Adjacent sequences:  A211154 A211155 A211156 * A211158 A211159 A211160 KEYWORD nonn AUTHOR Clark Kimberling, Apr 05 2012 STATUS approved

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Last modified September 28 20:03 EDT 2021. Contains 347717 sequences. (Running on oeis4.)