A211555 Number of (n+1)X(n+1) -9..9 symmetric matrices with every 2X2 subblock having sum zero and one, three or four distinct values

151, 1211, 9575, 75219, 586879, 4554563, 35183583, 270747747, 2076732739, 15885966079, 121240881187, 923512887871, 7023016209951, 53333227033923, 404532274018643, 3065221230865231, 23205080205698791, 175535780415251539

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..25

Example

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

Crossrefs

Sequence in context: A334836 A130870 A340436 * A143012 A375332 A250375

Adjacent sequences: A211552 A211553 A211554 * A211556 A211557 A211558

Keyword

nonn

Author

R. H. Hardin Apr 15 2012

Status

approved