A211058 Number of 2 X 2 matrices having all terms in {1,...,n} and nonnegative determinant.

1, 11, 48, 144, 337, 691, 1256, 2128, 3385, 5139, 7480, 10584, 14521, 19499, 25664, 33184, 42209, 53027, 65736, 80680, 98009, 117979, 140816, 166936, 196441, 229715, 267056, 308816, 355185, 406755, 463576, 526264, 595081, 670419

Offset

1,2

Comments

For a guide to related sequences, see A210000.

Links

Table of n, a(n) for n=1..34.

Mathematica

a = 1; b = n; z1 = 35;
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, 0, m}]
Table[c1[n, n^2], {n, 1, z1}]   (* A211058 *)

Crossrefs

Cf. A210000.

Sequence in context: A042984 A364579 A008780 * A239460 A226676 A101992

Adjacent sequences: A211055 A211056 A211057 * A211059 A211060 A211061

Keyword

nonn

Author

Clark Kimberling, Mar 31 2012

Status

approved