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 A211066 Number of 2 X 2 matrices having all terms in {1,...,n} and nonnegative even determinant. 4
 1, 8, 28, 96, 193, 448, 728, 1360, 1985, 3264, 4420, 6696, 8641, 12296, 15360, 20896, 25361, 33344, 39636, 50680, 59289, 74056, 85376, 104728, 119377, 144032, 162588, 193568, 216585, 254880, 283096, 329656, 363881, 419856, 460804 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS For a guide to related sequences, see A210000. LINKS Chai Wah Wu, Table of n, a(n) for n = 1..10000 FORMULA a(n) = (A211064(n) + A134506(n))/2. - Chai Wah Wu, Nov 28 2016 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] u[n_] := u[n] = Sum[c[n, 2 k], {k, 0, n^2}] v[n_] := v[n] = Sum[c[n, 2 k], {k, 1, n^2}] w[n_] := w[n] = Sum[c[n, 2 k - 1], {k, 1, n^2}] Table[u[n], {n, 1, z1}] (* A211066 *) Table[v[n], {n, 1, z1}] (* A211067 *) Table[w[n], {n, 1, z1}] (* A211068 *) CROSSREFS Cf. A210000. Sequence in context: A331454 A333278 A333283 * A095857 A184606 A054114 Adjacent sequences: A211063 A211064 A211065 * A211067 A211068 A211069 KEYWORD nonn AUTHOR Clark Kimberling, Mar 31 2012 STATUS approved

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Last modified December 5 03:48 EST 2023. Contains 367567 sequences. (Running on oeis4.)