|
| |
|
|
A211152
|
|
Number of 2 X 2 matrices having all terms in {-n,...,0,...,n} and determinant >= 2n.
|
|
2
|
|
|
|
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
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
|
OFFSET
|
1,1
|
|
|
COMMENTS
|
For a guide to related sequences, see A210000.
|
|
|
LINKS
|
Table of n, a(n) for n=1..27.
|
|
|
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 *)
|
|
|
CROSSREFS
|
Cf. A210000.
Sequence in context: A125710 A204296 A192790 * A093854 A345459 A269146
Adjacent sequences: A211149 A211150 A211151 * A211153 A211154 A211155
|
|
|
KEYWORD
|
nonn
|
|
|
AUTHOR
|
Clark Kimberling, Apr 05 2012
|
|
|
STATUS
|
approved
|
| |
|
|
