A193273 Number of n X n symmetric 0..7 arrays with no element equal to any horizontal or vertical neighbor and with new values 0..7 introduced in lower triangular row major order.

1, 2, 42, 12806, 71531470, 4359452409293, 1840118598465187309, 4839010680027431179628037, 78256880677789721019902991767596

Offset: 1

Author

R. H. Hardin Jul 20 2011

Keywords

• nonn

Examples

			Some solutions for 4X4
..0..1..0..4....0..1..2..1....0..1..2..1....0..1..3..4....0..1..2..1
..1..2..3..5....1..2..3..4....1..2..1..0....1..2..4..6....1..2..3..4
..0..3..4..2....2..3..2..1....2..1..3..4....3..4..5..7....2..3..2..5
..4..5..2..3....1..4..1..0....1..0..4..5....4..6..7..3....1..4..5..2