A195517 Number of lower triangles of an n X n -3..3 array with all row and column sums zero.

1, 1, 7, 175, 27267, 23663523, 122092290831, 3806404472713603, 731708552185212577507

Offset: 1

Author

R. H. Hardin Sep 20 2011

Keywords

• nonn

Comments

Column 3 of A195522

Examples

			Some solutions for n=4
..0........0........0........0........0........0........0........0
.-1.1......0.0......2-2......0.0.....-3.3.....-2.2.....-2.2......2-2
.-2-1.3....2-2.0....1.0-1....3.0-3....3-3.0....0-3.3....0-3.3....0.1-1
..3.0-3.0.-2.2.0.0.-3.2.1.0.-3.0.3.0..0.0.0.0..2.1-3.0..2.1-3.0.-2.1.1.0