A203365 Number of n X 2 0..2 arrays with every 1 immediately preceded by 0 to the left or above, and every 2 immediately preceded by both a 1 and a 0.

2, 9, 30, 110, 390, 1399, 4998, 17881, 63940, 228680, 817820, 2924801, 10460002, 37408329, 133784090, 478454630, 1711106370, 6119462399, 21885149998, 78268279361, 279912339880, 1001055838960, 3580095086040, 12803562326001

Offset

1,1

Comments

Column 2 of A203371.

Links

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

Formula

Empirical: a(n) = 2*a(n-1) +5*a(n-2) +2*a(n-3) +a(n-4).

Empirical g.f.: x*(2 + 5*x + 2*x^2 + x^3) / (1 - 2*x - 5*x^2 - 2*x^3 - x^4). - Colin Barker, Jun 04 2018

Example

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

Crossrefs

Cf. A203371.

Sequence in context: A261330 A101604 A234007 * A181954 A343565 A318101

Adjacent sequences: A203362 A203363 A203364 * A203366 A203367 A203368

Keyword

nonn

Author

R. H. Hardin, Dec 31 2011

Status

approved