A211059 Number of 2 X 2 matrices having all terms in {1,...,n} and positive determinant.

0, 5, 33, 112, 288, 605, 1145, 1968, 3176, 4861, 7161, 10152, 14040, 18917, 24961, 32352, 41312, 51949, 64585, 79320, 96472, 116277, 139025, 164840, 194184, 227261, 264385, 305840, 352096, 403245, 459945, 522312, 590840, 665917

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] - c[n, 0], {n, 1, z1}]   (* A211059 *)
2*%     (* A211056 *)

Crossrefs

Cf. A210000, A211056.

Sequence in context: A250225 A250273 A050830 * A292000 A146263 A359703

Adjacent sequences: A211056 A211057 A211058 * A211060 A211061 A211062

Keyword

nonn

Author

Clark Kimberling, Mar 31 2012

Status

approved