A211819 Number of (n+1)X(n+1) -10..10 symmetric matrices with every 2X2 subblock having sum zero and one, three or four distinct values

189, 1723, 15627, 141649, 1282035, 11589301, 104629731, 943364181, 8493714087, 76361644361, 685449576519, 6142764849673, 54955294341259, 490779912786661

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..14.

Example

Some solutions for n=3
..5..1..6.-1...-2.-3.-3..1...-8..6..1..9....2.-5.-2..0....8..0..1.-8
..1.-7..0.-5...-3..8.-2..4....6.-4.-3.-7...-5..8.-1..3....0.-8..7..0
..6..0..7.-2...-3.-2.-4..2....1.-3.10..0...-2.-1.-6..4....1..7.-6.-1
.-1.-5.-2.-3....1..4..2..0....9.-7..0-10....0..3..4.-2...-8..0.-1..8

Crossrefs

Sequence in context: A231394 A347383 A297229 * A266135 A133351 A267993

Adjacent sequences: A211816 A211817 A211818 * A211820 A211821 A211822

Keyword

nonn

Author

R. H. Hardin Apr 21 2012

Status

approved