A221769 Number of n X 2 arrays of occupancy after each element stays put or moves to some horizontal or vertical neighbor, without move-in move-out left turns.

3, 27, 240, 2127, 18828, 166581, 1473549, 13033908, 115285587, 1019699649, 9019211256, 79774585647, 705603080553, 6241031204616, 55201672045839, 488256584905473, 4318609990477032, 38197932848425719, 337859190101460441

Offset

1,1

Comments

Column 2 of A221773.

Links

R. H. Hardin, Table of n, a(n) for n = 1..210

Formula

Empirical: a(n) = 15*a(n-1) - 67*a(n-2) + 120*a(n-3) - 80*a(n-4) + 10*a(n-5).

Empirical g.f.: 3*x*(1 - x)*(1 - 5*x + 7*x^2 - x^3) / (1 - 15*x + 67*x^2 - 120*x^3 + 80*x^4 - 10*x^5). - Colin Barker, Aug 10 2018

Example

Some solutions for n=3:
..1..0....1..0....0..1....2..1....0..2....0..1....0..1....2..1....0..3....1..1
..0..3....2..2....2..2....2..0....1..0....0..3....2..1....0..0....1..1....1..2
..1..1....0..1....0..1....0..1....2..1....2..0....1..1....0..3....1..0....0..1

Crossrefs

Cf. A221773.

Sequence in context: A145608 A083713 A230179 * A065100 A035088 A344724

Adjacent sequences: A221766 A221767 A221768 * A221770 A221771 A221772

Keyword

nonn

Author

R. H. Hardin, Jan 25 2013

Status

approved