A209546 1/4 the number of (n+1) X 2 0..3 arrays with every 2 X 2 subblock having exactly two distinct clockwise edge differences.

7, 20, 61, 191, 603, 1909, 6049, 19173, 60777, 192665, 610761, 1936161, 6137793, 19457329, 61681409, 195535393, 619864097, 1965022785, 6229292161, 19747394881, 62600949633, 198450424449, 629105008769, 1994317286913, 6322158281217

Offset

1,1

Comments

Column 1 of A209553.

Links

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

Formula

Empirical: a(n) = 5*a(n-1) - 6*a(n-2) + 2*a(n-4).

Empirical g.f.: x*(7 - 15*x + 3*x^2 + 6*x^3) / ((1 - x)*(1 - 4*x + 2*x^2 + 2*x^3)). - Colin Barker, Jul 11 2018

Example

Some solutions for n=4:
..0..1....0..1....3..2....3..0....2..3....0..2....0..1....1..3....1..2....0..1
..3..2....1..2....0..1....0..3....3..2....2..0....3..2....3..1....0..1....1..2
..0..1....2..1....1..2....1..2....2..3....0..2....2..1....1..3....1..2....0..3
..3..2....1..2....0..1....2..3....3..2....2..0....1..2....3..1....2..3....3..0
..2..3....0..1....1..0....1..2....2..3....0..2....2..1....1..3....3..2....2..1

Crossrefs

Cf. A209553.

Sequence in context: A055267 A218843 A219422 * A222549 A196584 A301777

Adjacent sequences: A209543 A209544 A209545 * A209547 A209548 A209549

Keyword

nonn

Author

R. H. Hardin, Mar 10 2012

Status

approved