A211143 - OEIS

A211143

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

1, 20, 52, 84, 132, 156, 260, 228, 356, 372, 492, 404, 804, 508, 820, 844, 964, 716, 1396, 852, 1660, 1380, 1540, 1092, 2452, 1476, 1932, 1876, 2564, 1532, 3884, 1700, 3012, 2676, 3004, 2876, 4916, 2172, 3684, 3484, 5260

(list; graph; refs; listen; history; text; internal format)

OFFSET

0,2

COMMENTS

For a guide to related sequences, see A210000.

LINKS

Chai Wah Wu, Table of n, a(n) for n = 0..3000

MATHEMATICA

a = -n; b = n; z1 = 40;

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]

Table[c[n, n^2], {n, 0, z1}] (* A211143 *)

(1/4) Table[c[n, n^2], {n, 1, z1}] (* integers *)

CROSSREFS

Cf. A210000.

Sequence in context: A128905 A276135 A350115 * A183047 A209982 A205220

Adjacent sequences: A211140 A211141 A211142 * A211144 A211145 A211146

KEYWORD

nonn

AUTHOR

Clark Kimberling, Apr 03 2012

STATUS

approved