A195516 Number of lower triangles of an n X n -2..2 array with all row and column sums zero.

1, 1, 5, 65, 3753, 860017, 839301197, 3535646416019, 65638445025610187, 5443595184898837903553

Offset: 1

Author

R. H. Hardin Sep 20 2011

Keywords

• nonn

Comments

Column 2 of A195522

Examples

			Some solutions for n=4
..0........0........0........0........0........0........0........0
.-1.1.....-2.2.....-2.2......1-1......1-1......0.0......2-2......1-1
..0-2.2....1.0-1....2.0-2...-1-1.2....1-1.0...-1.2-1....0.2-2....0.0.0
..1.1-2.0..1-2.1.0..0-2.2.0..0.2-2.0.-2.2.0.0..1-2.1.0.-2.0.2.0.-1.1.0.0