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 A211065 Number of 2 X 2 matrices having all terms in {1,...,n} and odd determinant. 4
 0, 6, 40, 96, 288, 486, 1056, 1536, 2800, 3750, 6120, 7776, 11760, 14406, 20608, 24576, 33696, 39366, 52200, 60000, 77440, 87846, 110880, 124416, 154128, 171366, 208936, 230496, 277200, 303750, 360960, 393216, 462400, 501126, 583848 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS A211064(n)+A211065(n)=4^n. For a guide to related sequences, see A210000. LINKS Chai Wah Wu, Table of n, a(n) for n = 1..10000 FORMULA From Chai Wah Wu, Nov 27 2016: (Start) a(n) = (2*n + 1 -(-1)^n)^2*(6*n + 1 -(-1)^n)*(2*n - 1 + (-1)^n)/128. a(n) = a(n-1) + 4*a(n-2) - 4*a(n-3) - 6*a(n-4) + 6*a(n-5) + 4*a(n-6) - 4*a(n-7) - a(n-8) + a(n-9) for n > 9. G.f.: -2*x^2*(3*x^5 + 5*x^4 + 28*x^3 + 16*x^2 + 17*x + 3)/((x - 1)^5*(x + 1)^4). (End) 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_] := Sum[c[n, 2 k], {k, -2*n^2, 2*n^2}] v[n_] := Sum[c[n, 2 k - 1], {k, -2*n^2, 2*n^2}] Table[u[n], {n, 1, z1}] (* A211064 *) Table[v[n], {n, 1, z1}] (* A211065 *) CROSSREFS Cf. A210000. Sequence in context: A217074 A110424 A114079 * A002595 A263956 A229638 Adjacent sequences:  A211062 A211063 A211064 * A211066 A211067 A211068 KEYWORD nonn AUTHOR Clark Kimberling, Mar 31 2012 STATUS approved

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Last modified December 13 23:14 EST 2019. Contains 329974 sequences. (Running on oeis4.)