A232956 Number of 2 X n 0..3 arrays with no element x(i,j) adjacent to value 3-x(i,j) horizontally, diagonally or antidiagonally, and top left element zero.

4, 21, 129, 771, 4629, 27771, 166629, 999771, 5998629, 35991771, 215950629, 1295703771, 7774222629, 46645335771, 279872014629, 1679232087771, 10075392526629, 60452355159771, 362714130958629, 2176284785751771

Offset

1,1

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).

Conjectures from Colin Barker, Oct 06 2018: (Start)

G.f.: x*(4 + x) / ((1 + x)*(1 - 6*x)).

a(n) = (25*6^n - 18) / 42 for n even.

a(n) = (25*6^n + 18) / 42 for n odd.

(End)

Example

Some solutions for n=5:
..0..1..0..2..3....0..0..0..0..1....0..0..0..1..0....0..1..1..1..0
..3..2..0..2..2....0..1..1..0..2....0..0..1..1..0....0..0..0..1..0

Crossrefs

Row 2 of A232955.

Sequence in context: A293192 A300674 A371430 * A234268 A111177 A141052

Adjacent sequences: A232953 A232954 A232955 * A232957 A232958 A232959

Keyword

nonn

Author

R. H. Hardin, Dec 02 2013

Status

approved