A211717 Number of (n+1)X(n+1) -11..11 symmetric matrices with every 2X2 subblock having sum zero and one, three or four distinct values

231, 2333, 23349, 232503, 2302953, 22704347, 222873481, 2179177539, 21229916021, 206133137263, 1995258434861

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..11.

Example

Some solutions for n=3
.-1..2.-6..5....1.-4..3..1....1..3..0..4...-5..6.-5..7...-4..2.-6..4
..2.-3..7.-6...-4..7.-6..2....3.-7..4.-8....6.-7..6.-8....2..0..4.-2
.-6..7-11.10....3.-6..5.-1....0..4.-1..5...-5..6.-5..7...-6..4.-8..6
..5.-6.10.-9....1..2.-1.-3....4.-8..5.-9....7.-8..7.-9....4.-2..6.-4

Crossrefs

Sequence in context: A183672 A183664 A260302 * A029569 A152102 A183663

Adjacent sequences: A211714 A211715 A211716 * A211718 A211719 A211720

Keyword

nonn

Author

R. H. Hardin Apr 20 2012

Status

approved