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A211148 Number of 2x2 matrices having all terms in {-n,...,0,..,n} and positive determinant. 3
24, 248, 1056, 3008, 6904, 13624, 24448, 40576, 63640, 95288, 137632, 192384, 262392, 349688, 457088, 587520, 744344, 930104, 1149152, 1404160, 1699640, 2039544, 2428352, 2869312, 3368472, 3929912, 4558688, 5259712, 6039480 (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..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]

Table[c[n, 0], {n, 1, z1}]   (* A209981 *)

c1[n_, m_] := c1[n, m] = Sum[c[n, k], {k, 1, m}]

t = Table[c1[n, 2*n^2], {n, 1, z1}]   (* A211148 *)

2 t   (* A211149 *)

t/8   (* integers *)

CROSSREFS

Cf. A210000.

Sequence in context: A052652 A052732 A086603 * A000594 A022716 A181104

Adjacent sequences:  A211145 A211146 A211147 * A211149 A211150 A211151

KEYWORD

nonn

AUTHOR

Clark Kimberling, Apr 04 2012

STATUS

approved

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Last modified October 25 10:42 EDT 2014. Contains 248521 sequences.