A221624 Number of 2Xn arrays with each row a permutation of 1..n having at least as many downsteps as the preceding row

1, 3, 27, 410, 10055, 353654, 17052210, 1075295220, 86037489675, 8510611773950, 1020010974544958, 145633667181394028, 24424236713657975558, 4754016566455947216412, 1062903928921857001102308

Offset

1,2

Comments

Row 2 of A221623

Links

R. H. Hardin, Table of n, a(n) for n = 1..16

Example

Some solutions for n=3
..2..3..1....2..3..1....2..1..3....3..1..2....2..1..3....1..3..2....1..2..3
..3..2..1....1..3..2....2..3..1....2..1..3....2..1..3....2..3..1....1..2..3

Crossrefs

Sequence in context: A201696 A011781 A094577 * A108525 A136719 A279844

Adjacent sequences: A221621 A221622 A221623 * A221625 A221626 A221627

Keyword

nonn

Author

R. H. Hardin Jan 21 2013

Status

approved