A211447 Number of (n+1)X(n+1) -7..7 symmetric matrices with every 2X2 subblock having sum zero and one, three or four distinct values

91, 561, 3397, 20495, 123133, 738307, 4420961, 26449067, 158114037, 944443595, 5635861085, 33592371427, 199953831841, 1188364420259, 7050730029429, 41757312808091, 246836304140925, 1456269364652499, 8574736487657897

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..76

Example

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

Crossrefs

Sequence in context: A373526 A373521 A180942 * A188360 A165220 A020218

Adjacent sequences: A211444 A211445 A211446 * A211448 A211449 A211450

Keyword

nonn

Author

R. H. Hardin Apr 11 2012

Status

approved