A211062 - OEIS

%I #11 Jan 07 2017 02:39:32

%S 0,0,5,29,93,235,493,936,1622,2642,4057,6055,8608,12001,16297,21619,

%T 28127,36170,45624,57041,70350,85892,103748,124748,148174,175083,

%U 205683,239800,277908,321224,368301,421093,479209,543193,613374

%N Number of 2 X 2 matrices having all terms in {1,...,n} and determinant >= 2n.

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

%H Chai Wah Wu, <a href="/A211062/b211062.txt">Table of n, a(n) for n = 1..1000</a>

%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 d[n_, m_] := d[n, m] = Sum[c[n, k], {k, 0, m}]

%t Table[d[n, n^2] - d[n, 2 n - 1], {n, 1, z1}]

%Y Cf. A210000.

%K nonn

%O 1,3

%A _Clark Kimberling_, Mar 31 2012