A211147 Number of 2 X 2 matrices having all terms in {-n,...,0,...,n} and nonnegative determinant.

1, 57, 377, 1345, 3553, 7737, 14937, 26177, 42945, 66681, 99193, 142209, 198241, 269049, 357593, 466433, 598401, 756281, 944057, 1164289, 1421601, 1719161, 2061081, 2451329, 2895489, 3396729, 3960569, 4591937, 5296289, 6077881

Offset

0,2

Comments

It appears that all terms are of the form 8*k + 1.

For a guide to related sequences, see A210000.

Links

Table of n, a(n) for n=0..29.

Mathematica

a = -n; b = n; z1 = 30;
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, 2 n^2], {n, 0, z1}]

Crossrefs

Cf. A210000.

Sequence in context: A378064 A209517 A097200 * A237360 A076459 A268260

Adjacent sequences: A211144 A211145 A211146 * A211148 A211149 A211150

Keyword

nonn

Author

Clark Kimberling, Apr 03 2012

Status

approved