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

Table of n, a(n) for n=1..12.

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

Sequence in context: A291617 A304389 A211711 * A251445 A251283 A251276

Adjacent sequences: A211713 A211714 A211715 * A211717 A211718 A211719

Keyword

nonn

Author

R. H. Hardin Apr 20 2012

Status

approved