A211818 Number of (n+1)X(n+1) -10..10 symmetric matrices with every 2X2 subblock having sum zero and three or four distinct values

188, 1702, 15334, 138130, 1242978, 11177174, 100431854, 901725738, 8089235074, 72498715894, 649077462926, 5804421919322, 51840849262274, 462375098375406, 4118031964300046, 36620792527293818

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..16.

Example

Some solutions for n=3
..6..2..5..2..-10..9-10..3....9.-6..2.-5....9.-2..4.-2...-8..1.-3.-1
..2-10..3-10....9.-8..9.-2...-6..3..1..2...-2.-5..3.-5....1..6.-4..8
..5..3..4..3..-10..9-10..3....2..1.-5..2....4..3.-1..3...-3.-4..2.-6
..2-10..3-10....3.-2..3..4...-5..2..2..1...-2.-5..3.-5...-1..8.-6.10

Crossrefs

Sequence in context: A073586 A064115 A185241 * A204071 A089273 A035832

Adjacent sequences: A211815 A211816 A211817 * A211819 A211820 A211821

Keyword

nonn

Author

R. H. Hardin Apr 21 2012

Status

approved