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A211716

Number of (n+1)X(n+1) -11..11 symmetric matrices with every 2X2 subblock having sum zero and three or four distinct values.

230, 2312, 23056, 228984, 2263896, 22292220, 218675604, 2137539096, 20825437008, 202270208796, 1958886321268, 18919069642800

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

EXAMPLE

Some solutions for n=3

..4..3.-1.-6...-8..2.-8..2..-10..3.-4..0...-1..4.-3.-4...-7..8.-7..3

..3-10..8.-1....2..4..2..4....3..4.-3..7....4.-7..6..1....8.-9..8.-4

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

.-6.-1.-1..8....2..4..2..4....0..7.-6.10...-4..1.-2..9....3.-4..3..1

CROSSREFS

KEYWORD

nonn

AUTHOR

R. H. Hardin, Apr 20 2012

STATUS

approved

URL: https://oeis.org/A211716