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%I #9 Nov 27 2016 21:59:52
%S 0,6,40,96,288,486,1056,1536,2800,3750,6120,7776,11760,14406,20608,
%T 24576,33696,39366,52200,60000,77440,87846,110880,124416,154128,
%U 171366,208936,230496,277200,303750,360960,393216,462400,501126,583848
%N Number of 2 X 2 matrices having all terms in {1,...,n} and odd determinant.
%C A211064(n)+A211065(n)=4^n.
%C For a guide to related sequences, see A210000.
%H Chai Wah Wu, <a href="/A211065/b211065.txt">Table of n, a(n) for n = 1..10000</a>
%F From _Chai Wah Wu_, Nov 27 2016: (Start)
%F a(n) = (2*n + 1 -(-1)^n)^2*(6*n + 1 -(-1)^n)*(2*n - 1 + (-1)^n)/128.
%F 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.
%F 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).
%F (End)
%t a = 1; b = n; z1 = 35;
%t t[n_] := t[n] = Flatten[Table[w*z - x*y, {w, a, b}, {x, a, b}, {y, a, b}, {z, a, b}]]
%t c[n_, k_] := c[n, k] = Count[t[n], k]
%t u[n_] := Sum[c[n, 2 k], {k, -2*n^2, 2*n^2}]
%t v[n_] := Sum[c[n, 2 k - 1], {k, -2*n^2, 2*n^2}]
%t Table[u[n], {n, 1, z1}] (* A211064 *)
%t Table[v[n], {n, 1, z1}] (* A211065 *)
%Y Cf. A210000.
%K nonn
%O 1,2
%A _Clark Kimberling_, Mar 31 2012
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