|
%I #7 Jan 12 2017 01:56:32
%S 4,80,428,1428,3604,7924,14988,26244,43072,66844,98804,142652,197584,
%T 268800,357608,465888,596964,756036,942160,1163608,1420248,1717344,
%U 2056952,2451248,2891420,3392528,3958576
%N Number of 2 X 2 matrices having all terms in {-n,...,0,...,n} and determinant >= 2n.
%C For a guide to related sequences, see A210000.
%t a = -n; b = n; z1 = 27;
%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,2n-1],{n,1,z1}] (* A211152 *)
%t %/4 (* integers *)
%Y Cf. A210000.
%K nonn
%O 1,1
%A _Clark Kimberling_, Apr 05 2012
|
