A235888 Number of (n+1) X (3+1) 0..3 arrays with the minimum plus the upper median equal to the lower median plus the maximum in every 2 X 2 subblock.

352, 568, 1096, 2536, 6952, 21928, 76456, 283816, 1091752, 4280488, 16949416, 67453096, 269123752, 1075118248, 4297719976, 17185374376, 68730486952, 274899927208, 1099555668136, 4398134591656, 17592362205352, 70369096499368

Offset

1,1

Links

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

Formula

Empirical: a(n) = 7*a(n-1) - 14*a(n-2) + 8*a(n-3).

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

G.f.: 8*x*(44 - 237*x + 256*x^2) / ((1 - x)*(1 - 2*x)*(1 - 4*x)).

a(n) = 4*(42 + 21*2^n + 4^n).

(End)

Example

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

Crossrefs

Column 3 of A235893.

Sequence in context: A167820 A145633 A252250 * A256025 A256771 A256764

Adjacent sequences: A235885 A235886 A235887 * A235889 A235890 A235891

Keyword

nonn

Author

R. H. Hardin, Jan 16 2014

Status

approved