login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A211496 Number of (n+1)X(n+1) -4..4 symmetric matrices with every 2X2 subblock having sum zero and one, three or four distinct values 1
29, 105, 385, 1437, 5353, 19901, 73617, 271149, 994593, 3635837, 13253649, 48203469, 174998977, 634413757, 2297355217, 8312124813, 30054882625, 108619779773, 392421136145, 1417398932429, 5118773127873, 18484336915517 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Symmetry and 2X2 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..210

FORMULA

Empirical: a(n) = 12*a(n-1) -36*a(n-2) -86*a(n-3) +557*a(n-4) -82*a(n-5) -2844*a(n-6) +1812*a(n-7) +6764*a(n-8) -4000*a(n-9) -7184*a(n-10) +1824*a(n-11) +1408*a(n-12) -384*a(n-13)

EXAMPLE

Some solutions for n=3

.-2.-1..0..2....0.-2..1..2...-4..1.-4..2...-2..3.-2.-1....4.-1..2.-1

.-1..4.-3..1...-2..4.-3..0....1..2..1..1....3.-4..3..0...-1.-2..1.-2

..0.-3..2..0....1.-3..2..1...-4..1.-4..2...-2..3.-2.-1....2..1..0..1

..2..1..0.-2....2..0..1.-4....2..1..2..0...-1..0.-1..4...-1.-2..1.-2

CROSSREFS

Sequence in context: A126554 A258721 A009406 * A233049 A233050 A142176

Adjacent sequences:  A211493 A211494 A211495 * A211497 A211498 A211499

KEYWORD

nonn

AUTHOR

R. H. Hardin Apr 13 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 | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified May 15 23:51 EDT 2022. Contains 353687 sequences. (Running on oeis4.)