A211718 Number of (n+1)X(n+1) -11..11 symmetric matrices with every 2X2 subblock having sum zero and two, three or four distinct values

264, 3038, 35014, 404214, 4673910, 54129486, 627846218, 7293174926, 84839745786, 988267636274, 11526926036602, 134612671646418, 1573840216457142, 18420681939043482, 215818650878928686, 2530919496941096390

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..33

Example

Some solutions for n=3
.-8..4..1..0...-3.-3.-3..0....8.-9..7.-5...-3.-3.-1..2...-2..6.-1.-1
..4..0.-5..4...-3..9.-3..6...-9.10.-8..6...-3..9.-5..4....6-10..5.-3
..1.-5.10.-9...-3.-3.-3..0....7.-8..6.-4...-1.-5..1..0...-1..5..0.-2
..0..4.-9..8....0..6..0..3...-5..6.-4..2....2..4..0.-1...-1.-3.-2..4

Crossrefs

Sequence in context: A014745 A004533 A231301 * A331769 A288995 A092724

Adjacent sequences: A211715 A211716 A211717 * A211719 A211720 A211721

Keyword

nonn

Author

R. H. Hardin Apr 20 2012

Status

approved