A211152 Number of 2 X 2 matrices having all terms in {-n,...,0,...,n} and determinant >= 2n.

4, 80, 428, 1428, 3604, 7924, 14988, 26244, 43072, 66844, 98804, 142652, 197584, 268800, 357608, 465888, 596964, 756036, 942160, 1163608, 1420248, 1717344, 2056952, 2451248, 2891420, 3392528, 3958576

Offset: 1

Author

Clark Kimberling, Apr 05 2012

Keywords

• nonn

Comments

For a guide to related sequences, see A210000.

Crossrefs

Cf. A210000.

Programs

Mathematica

a = -n; b = n; z1 = 27;
t[n_] := t[n] = Flatten[Table[w*z - x*y, {w, a, b}, {x, a, b}, {y, a, b}, {z, a, b}]]
c[n_, k_] := c[n, k] = Count[t[n], k]
c1[n_, m_] := c1[n, m] = Sum[c[n, k], {k, -2*n^2, m}]
Table[c1[n,2*n^2]-c1[n,2n-1],{n,1,z1}] (* A211152 *)
%/4  (* integers *)