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A211717 Number of (n+1)X(n+1) -11..11 symmetric matrices with every 2X2 subblock having sum zero and one, three or four distinct values 0
231, 2333, 23349, 232503, 2302953, 22704347, 222873481, 2179177539, 21229916021, 206133137263, 1995258434861 (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

Table of n, a(n) for n=1..11.

EXAMPLE

Some solutions for n=3

.-1..2.-6..5....1.-4..3..1....1..3..0..4...-5..6.-5..7...-4..2.-6..4

..2.-3..7.-6...-4..7.-6..2....3.-7..4.-8....6.-7..6.-8....2..0..4.-2

.-6..7-11.10....3.-6..5.-1....0..4.-1..5...-5..6.-5..7...-6..4.-8..6

..5.-6.10.-9....1..2.-1.-3....4.-8..5.-9....7.-8..7.-9....4.-2..6.-4

CROSSREFS

Sequence in context: A183672 A183664 A260302 * A029569 A152102 A183663

Adjacent sequences:  A211714 A211715 A211716 * A211718 A211719 A211720

KEYWORD

nonn

AUTHOR

R. H. Hardin Apr 20 2012

STATUS

approved

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Last modified August 11 00:55 EDT 2022. Contains 356046 sequences. (Running on oeis4.)