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A211157 Number of 2 X 2 matrices having all terms in {-n,...,0,..,n} and positive even determinant. 4
4, 164, 528, 1968, 3844, 8836, 14144, 26176, 37540, 61188, 82192, 123120, 157924, 223268, 276608, 374272, 452420, 591524, 700752, 891760, 1038980, 1293700, 1487744, 1818112, 2067172 (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..25.

MATHEMATICA

a = -n; b = n; z1 = 25;

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]

u[n_] := u[n] = Sum[c[n, 2 k], {k, 0, 2*n^2}]

v[n_] := v[n] = Sum[c[n, 2 k], {k, 1, 2*n^2}]

w[n_] := w[n] = Sum[c[n, 2 k - 1], {k, 1, 2*n^2}]

u1 = Table[u[n], {n, 1, z1}] (* A211156 *)

v1 = Table[v[n], {n, 1, z1}] (* A211157 *)

w1 = Table[w[n], {n, 1, z1}] (* A211158 *)

(u1 - 1)/4 (* integers *)

v1/4 (* integers *)

w1/4 (* integers *)

CROSSREFS

Cf. A210000.

Sequence in context: A306350 A125532 A229405 * A185857 A221654 A159011

Adjacent sequences:  A211154 A211155 A211156 * A211158 A211159 A211160

KEYWORD

nonn

AUTHOR

Clark Kimberling, Apr 05 2012

STATUS

approved

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Last modified September 28 20:03 EDT 2021. Contains 347717 sequences. (Running on oeis4.)