A211471 Number of (n+1)X(n+1) -8..8 symmetric matrices with every 2X2 subblock having sum zero and three or four distinct values

120, 856, 6040, 42492, 297572, 2076768, 14447284, 100224428, 693541160, 4788481556, 32994512924, 226924908072, 1558056553740, 10680681136996, 73109657722272, 499746329784652, 3411594843779188, 23261004734670688

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..30

Example

Some solutions for n=3
.-7..4.-3..6....8.-1..6..0....4.-6..4.-5....6..1..2.-4....1..2..2.-4
..4.-1..0.-3...-1.-6..1.-7...-6..8.-6..7....1.-8..5.-3....2.-5..1..1
.-3..0..1..2....6..1..4..2....4.-6..4.-5....2..5.-2..0....2..1..3.-5
..6.-3..2.-5....0.-7..2.-8...-5..7.-5..6...-4.-3..0..2...-4..1.-5..7

Crossrefs

Sequence in context: A235551 A300664 A029573 * A250519 A250512 A011245

Adjacent sequences: A211468 A211469 A211470 * A211472 A211473 A211474

Keyword

nonn

Author

R. H. Hardin Apr 12 2012

Status

approved