login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A211156 Number of 2 X 2 matrices having all terms in {-n,...,0,..,n} and even nonnegative determinant. 4
37, 293, 817, 2513, 4677, 10149, 15873, 28545, 40581, 65093, 86769, 128977, 164581, 231173, 285953, 385153, 464357, 605477, 715889, 909201, 1058501, 1315237, 1510721, 1844289, 2095429 (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: A086840 A190418 A200889 * A217642 A197340 A165373

Adjacent sequences:  A211153 A211154 A211155 * A211157 A211158 A211159

KEYWORD

nonn

AUTHOR

Clark Kimberling, Apr 05 2012

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified October 22 22:35 EDT 2021. Contains 348180 sequences. (Running on oeis4.)