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A180840 Number of nX2 arrays containing 2 indistinguishable copies of 1..n with lexicographical ordering of rows strictly increasing and columns strictly decreasing 0
1, 0, 2, 17, 131, 1220, 13796, 183095, 2790353, 48045596, 922507880, 19543670381, 452869998215 (list; graph; refs; listen; history; text; internal format)
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

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Last modified August 19 22:59 EDT 2022. Contains 356231 sequences. (Running on oeis4.)