A180840 Number of nX2 arrays containing 2 indistinguishable copies of 1..n with lexicographical ordering of rows strictly increasing and columns strictly decreasing

1, 0, 2, 17, 131, 1220, 13796, 183095, 2790353, 48045596, 922507880, 19543670381, 452869998215

Offset

1,3

Comments

Column 2 of A180843

Links

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

Example

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

Crossrefs

Sequence in context: A073510 A291390 A007354 * A261120 A077243 A037525

Adjacent sequences: A180837 A180838 A180839 * A180841 A180842 A180843

Keyword

nonn

Author

R. H. Hardin Sep 20 2010

Status

approved