login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A211328 Number of (n+1) X (n+1) -3..3 symmetric matrices with every 2 X 2 subblock having sum zero and two, three or four distinct values. 1
24, 86, 310, 1134, 4190, 15582, 58130, 217014, 809418, 3013130, 11188738, 41433570, 153004862, 563461506, 2069583806, 7582810302, 27719202126, 101113824446, 368123385634, 1337824919574, 4853929237946, 17584750606794, 63618436617746 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Symmetry and 2 X 2 block sums zero implies that the diagonal x(i,i) are equal modulo 2 and x(i,j) = (x(i,i)+x(j,j))/2*(-1)^(i-j).

LINKS

R. H. Hardin, Table of n, a(n) for n = 1..90

FORMULA

Empirical: a(n) = 13*a(n-1) - 63*a(n-2) + 130*a(n-3) - 65*a(n-4) - 115*a(n-5) + 69*a(n-6) + 68*a(n-7) + 12*a(n-8).

Empirical g.f.: 2*x*(12 - 113*x + 352*x^2 - 299*x^3 - 321*x^4 + 302*x^5 + 249*x^6 + 42*x^7) / ((1 - 2*x)*(1 - 3*x)*(1 - 2*x - x^2)*(1 - 3*x - x^2)*(1 - 3*x - 2*x^2)). - Colin Barker, Jul 17 2018

EXAMPLE

Some solutions for n=3:

..1.-2.-1..1...-1..1.-1.-1....1..1.-1.-2...-3..1..0..2....2..0..1..0

.-2..3..0..0....1.-1..1..1....1.-3..3..0....1..1.-2..0....0.-2..1.-2

.-1..0.-3..3...-1..1.-1.-1...-1..3.-3..0....0.-2..3.-1....1..1..0..1

..1..0..3.-3...-1..1.-1..3...-2..0..0..3....2..0.-1.-1....0.-2..1.-2

CROSSREFS

Sequence in context: A168538 A007201 A228874 * A304375 A044211 A044592

Adjacent sequences:  A211325 A211326 A211327 * A211329 A211330 A211331

KEYWORD

nonn

AUTHOR

R. H. Hardin, Apr 07 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 19 16:17 EDT 2019. Contains 328223 sequences. (Running on oeis4.)