A211446 Number of (n+1) X (n+1) -7..7 symmetric matrices with every 2 X 2 subblock having sum zero and three or four distinct values.

90, 548, 3296, 19844, 119260, 716592, 4303756, 25835124, 154970728, 928644692, 5557654436, 33210094112, 198105342332, 1179507539876, 7008630194584, 41558569591508, 245903742193060, 1451916609628912, 8554514693602716

Offset

1,1

Comments

Symmetry and 2 X 2 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..69

Example

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

Crossrefs

Sequence in context: A233638 A289792 A156738 * A203787 A203780 A295982

Adjacent sequences: A211443 A211444 A211445 * A211447 A211448 A211449

Keyword

nonn

Author

R. H. Hardin Apr 11 2012

Status

approved