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

Author

R. H. Hardin Jan 21 2013

Keywords

• nonn

Comments

Row 2 of A221623

Examples

			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
		

Links

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