A180836 Number of nX2 arrays containing 2 indistinguishable copies of 1..n with rows and columns in lexicographically strictly increasing order

1, 1, 9, 72, 678, 7719, 102963, 1573764, 27143466, 521698683, 11059018599, 256349691978, 6451098232944

Offset

1,3

Comments

Column 2 of A180839

Links

Table of n, a(n) for n=1..13.

Example

Some solutions for 4X2
..1..1....1..1....1..1....1..1....1..1....1..1....1..1....1..1....1..1....1..3
..2..3....2..3....2..3....2..3....2..3....2..2....2..4....2..4....2..4....1..4
..3..2....3..4....2..4....2..4....4..2....3..4....3..3....3..2....3..2....3..2
..4..4....4..2....4..3....3..4....4..3....4..3....4..2....4..3....3..4....4..2
...
..1..3....1..3....1..3....1..3....1..3....1..3....1..3....1..3....1..3....1..3
..1..4....1..4....1..4....1..4....1..4....3..2....2..1....2..1....2..1....2..1
..2..3....2..3....2..2....2..2....2..4....4..1....3..2....3..4....2..3....2..4
..4..2....2..4....4..3....3..4....3..2....4..2....4..4....4..2....4..4....4..3
...
..1..3....1..3....1..3....1..3....1..3....1..3....1..3....1..3....1..3....1..2
..2..1....2..1....2..3....2..3....2..2....2..2....2..2....2..4....2..4....1..3
..2..4....4..2....2..4....4..1....3..1....3..4....4..1....3..1....3..2....3..2
..3..4....4..3....4..1....4..2....4..4....4..1....4..3....4..2....4..1....4..4

Crossrefs

Sequence in context: A127053 A001809 A006135 * A218126 A133672 A043079

Adjacent sequences: A180833 A180834 A180835 * A180837 A180838 A180839

Keyword

nonn

Author

R. H. Hardin Sep 20 2010

Status

approved