A224128 Number of n X 3 0..1 arrays with rows nondecreasing and antidiagonals unimodal.

4, 16, 58, 208, 748, 2692, 9688, 34864, 125464, 451504, 1624816, 5847184, 21042112, 75723712, 272504992, 980656768, 3529064512, 12699954496, 45703002496, 164470230016, 591874824064, 2129964841216, 7665050176768, 27584020672768

Offset

1,1

Comments

Column 3 of A224133.

Links

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

Formula

Empirical: a(n) = 4*a(n-1) - 2*a(n-2) + 2*a(n-3).

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

Example

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

Crossrefs

Cf. A224133.

Sequence in context: A255299 A123889 A180143 * A123893 A134762 A207276

Adjacent sequences: A224125 A224126 A224127 * A224129 A224130 A224131

Keyword

nonn

Author

R. H. Hardin, Mar 31 2013

Status

approved