A206505 Number of (n+1) X 2 0..2 arrays with the number of clockwise edge increases in 2 X 2 subblocks nondecreasing rightwards and downwards.

81, 549, 3399, 19797, 111495, 614367, 3337695, 17958813, 95989473, 510679479, 2707979133, 14326037895, 75662455155, 399129270627, 2103642300213, 11080520280189, 58338276097647, 307048060430277, 1615687942238055

Offset

1,1

Comments

Column 1 of A206512.

Links

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

Formula

Empirical: a(n) = 9*a(n-1) - 18*a(n-2) - 15*a(n-3) + 36*a(n-4) - 20*a(n-5) + 11*a(n-6) - 2*a(n-7).

Empirical g.f.: 3*x*(27 - 60*x - 28*x^2 + 101*x^3 - 59*x^4 + 33*x^5 - 6*x^6) / ((1 - x)*(1 - 4*x + x^2 - x^3)*(1 - 4*x - 7*x^2 + 2*x^3)). - Colin Barker, Jun 17 2018

Example

Some solutions for n=4:
..2..2....1..2....1..2....1..2....2..2....2..1....2..1....0..0....1..2....2..0
..1..0....1..2....0..1....1..2....2..1....2..0....0..2....2..1....2..2....2..2
..0..1....2..0....2..2....1..0....2..1....0..1....1..0....0..2....1..2....0..2
..1..2....0..1....1..0....2..1....1..1....0..2....2..1....2..0....1..0....2..0
..0..2....2..2....2..1....1..2....2..1....1..0....1..2....2..1....2..1....1..2

Crossrefs

Cf. A206512.

Sequence in context: A206512 A235833 A235588 * A235584 A231973 A205894

Adjacent sequences: A206502 A206503 A206504 * A206506 A206507 A206508

Keyword

nonn

Author

R. H. Hardin, Feb 08 2012

Status

approved