%I #6 Jan 12 2017 01:26:57

%S 0,20,184,804,2284,5408,10780,20084,33664,53840,81124,119156,167872,

%T 231096,309816,409128,527088,673112,842776,1049352,1285760,1561932,

%U 1879908,2247884,2662000,3134360,3662256,4264796,4926892,5673180

%N Number of 2 X 2 matrices having all terms in {-n,...,0,..,n} and determinant >= 3n.

%C For a guide to related sequences, see A210000.

%t a = -n; b = n; z1 = 30;

%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, -2*n^2, m}]

%t Table[c1[n,2*n^2]-c1[n,3n-1],{n,1,z1}] (* A211153 *)

%t %/4 (* integers *)

%Y Cf. A210000.

%K nonn

%O 1,2

%A _Clark Kimberling_, Apr 05 2012