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%I #7 Jan 14 2017 01:36:34
%S 1,10,36,91,179,330,516,802,1150,1615,2119,2873,3595,4558,5653,6967,
%T 8245,10020,11642,13846,16053,18524,20944,24393,27405,30924,34637,
%U 39035,42961,48396,52906,58687,64326,70457,76722,84824,91318,99045
%N Number of 2 X 2 matrices having all terms in {1,...,n} and determinant in the closed interval [0,n].
%C For a guide to related sequences, see A210000.
%t a = 1; b = n; z1 = 40;
%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 c1[n_, m_] := c1[n, m] = Sum[c[n, k], {k, 0, m}]
%t Table[c1[n, n], {n, 1, z1}] (* A211057 *)
%Y Cf. A210000.
%K nonn
%O 1,2
%A _Clark Kimberling_, Mar 31 2012
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