A183246 Number of permutations of 1..2*n+3 with each element displaced by at least n.

44, 206, 1168, 6984, 41808, 250464, 1501248, 9001344, 53983488, 323802624, 1942422528, 11652962304, 69911482368, 419443728384, 2516561707008, 15098967588864, 90592194920448, 543546727071744, 3261254592626688

Offset

1,1

Comments

Row 4 of A183244.

Links

R. H. Hardin, Table of n, a(n) for n = 1..66

Formula

Empirical (for n>=3): 289/9*6^(n-1) + 3*4^(n-2). - Vaclav Kotesovec, Nov 27 2012

Conjectures from Colin Barker, Mar 27 2018: (Start)

G.f.: 2*x*(22 - 117*x + 82*x^2 + 124*x^3) / ((1 - 4*x)*(1 - 6*x)).

a(n) = 10*a(n-1) - 24*a(n-2) for n>4.

(End)

Example

Some permutations of 1-7 with minimum displacement 2:
(4,5,6,1,7,3,2) (3,6,5,7,2,4,1) (7,6,1,2,3,4,5) (6,4,1,2,7,3,5) (5,6,7,1,3,2,4)
(3,7,5,6,1,4,2) (5,6,1,2,7,3,4) (6,5,7,2,1,4,3) (6,5,1,7,3,4,2) (6,5,1,7,2,4,3)
(7,5,6,1,2,3,4) (5,7,1,6,2,3,4) (3,4,6,7,1,2,5) (4,6,5,7,2,1,3) (7,4,5,6,1,2,3)
(6,4,7,2,1,3,5) (4,6,1,7,3,2,5) (5,6,1,2,7,4,3) (5,4,6,7,1,3,2) (3,5,7,6,2,1,4)

Crossrefs

Cf. A183244.

Sequence in context: A238249 A189547 A026908 * A186248 A215677 A122235

Adjacent sequences: A183243 A183244 A183245 * A183247 A183248 A183249

Keyword

nonn

Author

R. H. Hardin, Jan 03 2011

Status

approved