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A210285 Number of 2 X 2 matrices with all elements in {0,1,...,n} and determinant floor(n/2).

%I A210285 #9 Nov 25 2016 12:21:57
%S A210285 1,10,7,15,36,52,65,89,155,179,153,193,374,422,287,319,617,681,584,
%T A210285 656,914,962,639,727,1705,1785,889,961,1672,1784,1768,1888,2496,2576,
%U A210285 1483,1579,3460,3604,1843,1939,4177,4337,3298,3466,3886,3982
%N A210285 Number of 2 X 2 matrices with all elements in {0,1,...,n} and determinant floor(n/2).
%C A210285 See A210000 for a guide to related sequences.
%H A210285 Chai Wah Wu, <a href="/A210285/b210285.txt">Table of n, a(n) for n = 0..3000</a>
%t A210285 a = 0; b = n; z1 = 45;
%t A210285 t[n_] := t[n] = Flatten[Table[w*z - x*y, {w, a, b}, {x, a, b}, {y, a, b}, {z, a, b}]]
%t A210285 c[n_, k_] := c[n, k] = Count[t[n], k]
%t A210285 Table[c[n, Floor[n/2]], {n, 0, z1}]   (* A210285 *)
%Y A210285 Cf. A210000.
%K A210285 nonn
%O A210285 0,2
%A A210285 _Clark Kimberling_, Mar 19 2012