A211060 - OEIS

%I #11 Jan 07 2017 02:39:26

%S 0,1,12,53,158,361,740,1326,2235,3524,5361,7711,10926,14941,20011,

%T 26217,33964,43007,54094,66834,81956,99455,119872,142543,169036,

%U 198791,232419,269781,312224,358359,410670,467577,530755,599962,676006

%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="/A211060/b211060.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 c1[n_, m_] := c1[n, m] = Sum[c[n, k], {k, 0, m}]

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

%Y Cf. A210000.

%K nonn

%O 1,3

%A _Clark Kimberling_, Mar 31 2012