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A211472 Number of (n+1)X(n+1) -8..8 symmetric matrices with every 2X2 subblock having sum zero and one, three or four distinct values 1
121, 873, 6225, 44205, 312209, 2195485, 15376453, 107305341, 746401305, 5176610637, 35805913289, 247058995669, 1700863663801, 11685223911345, 80125271642765, 548435823880377, 3747645664538313, 25569088975353613 (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..31

EXAMPLE

Some solutions for n=3

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

..4.-7..4.-1...-3..4.-3..5....1.-2..3.-5...-4..8.-2..7....2..0.-2..1

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

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

CROSSREFS

Sequence in context: A238250 A293588 A203959 * A223389 A243810 A302561

Adjacent sequences:  A211469 A211470 A211471 * A211473 A211474 A211475

KEYWORD

nonn

AUTHOR

R. H. Hardin Apr 12 2012

STATUS

approved

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Last modified August 5 05:22 EDT 2020. Contains 336209 sequences. (Running on oeis4.)