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!)
A211497 Number of (n+1)X(n+1) -4..4 symmetric matrices with every 2X2 subblock having sum zero and two, three or four distinct values 1
40, 180, 808, 3636, 16396, 74104, 335660, 1523420, 6925768, 31527492, 143656108, 654965928, 2986993420, 13622286844, 62110476152, 283072002980, 1289383564204, 5869109209272, 26695147549612, 121321864635996, 550906942638568 (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..162

FORMULA

Empirical: a(n) = 21*a(n-1) -177*a(n-2) +742*a(n-3) -1477*a(n-4) +665*a(n-5) +1725*a(n-6) -952*a(n-7) -1462*a(n-8) -476*a(n-9) -48*a(n-10)

EXAMPLE

Some solutions for n=3

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

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

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

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

CROSSREFS

Sequence in context: A264547 A327430 A251210 * A251203 A187510 A187379

Adjacent sequences:  A211494 A211495 A211496 * A211498 A211499 A211500

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 21 14:54 EDT 2022. Contains 353921 sequences. (Running on oeis4.)