A251251 Number of (n+1) X (1+1) 0..1 arrays with every 2 X 2 subblock having a single 1 or two 1s on the same edge.

8, 18, 38, 84, 180, 394, 850, 1852, 4008, 8714, 18886, 41020, 88964, 193138, 419010, 909460, 1973352, 4282722, 9293318, 20168132, 43765364, 94976442, 206104402, 447268364, 970605128, 2106305818, 4570852838, 9919165164, 21525417860

Offset

1,1

Links

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

Formula

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

Empirical g.f.: 2*x*(4 + 5*x - 2*x^2) / (1 - x - 3*x^2 + x^3). - Colin Barker, Nov 27 2018

Example

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

Crossrefs

Column 1 of A251258.

Sequence in context: A129958 A082227 A134062 * A067563 A211477 A123134

Adjacent sequences: A251248 A251249 A251250 * A251252 A251253 A251254

Keyword

nonn

Author

R. H. Hardin, Dec 01 2014

Status

approved