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%I #8 Jan 10 2017 22:07:39
%S 1,16,69,176,375,650,1107,1626,2413,3326,4527,5782,7689,9436,11753,
%T 14354,17491,20458,24623,28334,33425,38438,44031,49450,57323,64028,
%U 71849,80078,89857,98468,110545,120388,133117,145382,158699,172256
%N Number of 2 X 2 matrices having all elements in {0,1,...,n} and determinant in the closed interval [-n,n].
%C For a guide to related sequences, see A210000.
%t a = 0; 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, -n, m}]
%t Table[c1[n, n], {n, 0, z1}] (* A211031 *)
%Y Cf. A210000, A211032.
%K nonn
%O 0,2
%A _Clark Kimberling_, Mar 30 2012