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A210368 Number of 2 X 2 matrices with all elements in {0,1,...,n} and determinant >= 3n.

%I A210368 #11 Jul 28 2017 09:46:31
%S A210368 1,0,0,7,35,104,252,509,997,1688,2751,4175,6240,8872,12324,16639,
%T A210368 22196,28668,36931,46332,58184,71524,87183,105334,126524,150233,
%U A210368 177448,207751,242948,281139,324739
%N A210368 Number of 2 X 2 matrices with all elements in {0,1,...,n} and determinant >= 3n.
%C A210368 See A210000 for a guide to related sequences.
%H A210368 Chai Wah Wu, <a href="/A210368/b210368.txt">Table of n, a(n) for n = 0..3000</a>
%t A210368 a = 0; b = n; z1 = 30;
%t A210368 t[n_] := t[n] = Flatten[Table[w*z - x*y, {w, a, b}, {x, a, b}, {y, a, b}, {z, a, b}]]
%t A210368 c[n_, k_] := c[n, k] = Count[t[n], k]
%t A210368 c1[n_, m_] := c1[n, m] = Sum[c[n, k], {k, 0, m}]
%t A210368 Table[c1[n, n^2] - c1[n, 3 n - 1], {n, 0, z1}]
%Y A210368 Cf. A210000.
%K A210368 nonn
%O A210368 0,4
%A A210368 _Clark Kimberling_, Mar 20 2012