A211061 - OEIS

%I #11 Jan 07 2017 02:39:29

%S 0,3,19,69,181,411,785,1419,2334,3674,5478,7994,11093,15249,20347,

%T 26660,34253,43661,54463,67637,82614,100217,120415,143935,169815,

%U 199883,233505,271344,313103,360519,411681,469615,532407,601850,677764

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

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

%H Chai Wah Wu, <a href="/A211061/b211061.txt">Table of n, a(n) for n = 1..1000</a>

%t a = 1; b = n; z1 = 35;

%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^2] - c1[n, n - 1], {n, 1, z1}]

%Y Cf. A210000.

%K nonn

%O 1,2

%A _Clark Kimberling_, Mar 31 2012