A231247 Number of 2 X n 0..3 arrays x(i,j) with each element horizontally, diagonally or antidiagonally next to at least one element with value (x(i,j)+1) mod 4, no adjacent elements equal, and upper left element zero.

0, 2, 14, 44, 146, 572, 2258, 8660, 33026, 126476, 485138, 1859972, 7128386, 27320636, 104717714, 401375924, 1538429186, 5896613228, 22601043602, 86627271908, 332032579394, 1272643303580, 4877897825810, 18696431115284

Offset

1,2

Links

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

Formula

Empirical: a(n) = 4*a(n-1) - 3*a(n-2) + 8*a(n-3) + 4*a(n-4) for n>5.

Empirical g.f.: 2*x^2*(1 + 3*x - 3*x^2 - 2*x^3) / (1 - 4*x + 3*x^2 - 8*x^3 - 4*x^4). - Colin Barker, Sep 27 2018

Example

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

Crossrefs

Row 2 of A231246.

Sequence in context: A212902 A091405 A085929 * A318764 A036659 A079937

Adjacent sequences: A231244 A231245 A231246 * A231248 A231249 A231250

Keyword

nonn

Author

R. H. Hardin, Nov 06 2013

Status

approved