A235878 Number of (n+1) X (2+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.

51, 105, 231, 537, 1311, 3345, 8871, 24297, 68271, 195585, 568311, 1668057, 4930431, 14643825, 43636551, 130319817, 389779791, 1166980065, 3496221591, 10479227577, 31418808351, 94218676305, 282580531431, 847590599337, 2542469808111

Offset

1,1

Links

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

Formula

Empirical: a(n) = 6*a(n-1) - 11*a(n-2) + 6*a(n-3).

Conjectures from Colin Barker, Oct 19 2018: (Start)

G.f.: 3*x*(17 - 67*x + 54*x^2) / ((1 - x)*(1 - 2*x)*(1 - 3*x)).

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

(End)

Example

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

Crossrefs

Column 2 of A235884.

Sequence in context: A044521 A160847 A260517 * A015705 A359088 A044238

Adjacent sequences: A235875 A235876 A235877 * A235879 A235880 A235881

Keyword

nonn

Author

R. H. Hardin, Jan 16 2014

Status

approved