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

121, 873, 6225, 44205, 312209, 2195485, 15376453, 107305341, 746401305, 5176610637, 35805913289, 247058995669, 1700863663801, 11685223911345, 80125271642765, 548435823880377, 3747645664538313, 25569088975353613

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: A365969 A203959 A362319 * A223389 A243810 A302561

Adjacent sequences: A211469 A211470 A211471 * A211473 A211474 A211475

Keyword

nonn

Author

R. H. Hardin Apr 12 2012

Status

approved