A235877 Number of (n+1) X (1+1) 0..2 arrays with the minimum plus the upper median equal to the lower median plus the maximum in every 2 X 2 subblock.

21, 51, 129, 339, 921, 2571, 7329, 21219, 62121, 183291, 543729, 1618899, 4832121, 14447211, 43243329, 129533379, 388206921, 1163834331, 3489930129, 10466644659, 31393642521, 94168344651, 282479868129, 847389272739, 2542067154921

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 19 2018: (Start)

G.f.: 3*x*(7 - 18*x) / ((1 - 2*x)*(1 - 3*x)).

a(n) = 3*(2^(1+n) + 3^n).

(End)

Example

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

Crossrefs

Column 1 of A235884.

Sequence in context: A224334 A305002 A242236 * A146838 A146593 A176588

Adjacent sequences: A235874 A235875 A235876 * A235878 A235879 A235880

Keyword

nonn

Author

R. H. Hardin, Jan 16 2014

Status

approved