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Number of nX2 arrays containing 2 indistinguishable copies of 1..n with lexicographical ordering of rows strictly increasing and columns strictly decreasing
0

%I #2 Mar 31 2012 12:35:48

%S 1,0,2,17,131,1220,13796,183095,2790353,48045596,922507880,

%T 19543670381,452869998215

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

%C Column 2 of A180843

%e All solutions for 4X2

%e ..1..1....1..1....3..1....2..1....2..1....2..1....2..1....2..1....2..1....2..1

%e ..3..2....3..2....3..2....3..1....3..1....3..1....3..3....3..2....3..2....2..3

%e ..3..4....4..2....4..1....3..2....3..4....4..2....4..1....3..4....4..1....3..1

%e ..4..2....4..3....4..2....4..4....4..2....4..3....4..2....4..1....4..3....4..4

%e ...

%e ..2..1....2..1....2..1....2..1....2..1....2..2....2..2

%e ..2..3....2..3....2..4....2..4....2..4....3..1....3..1

%e ..3..4....4..1....3..1....3..1....3..3....3..4....4..1

%e ..4..1....4..3....4..3....3..4....4..1....4..1....4..3

%K nonn

%O 1,3

%A _R. H. Hardin_ Sep 20 2010