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A224128 Number of n X 3 0..1 arrays with rows nondecreasing and antidiagonals unimodal. 1
4, 16, 58, 208, 748, 2692, 9688, 34864, 125464, 451504, 1624816, 5847184, 21042112, 75723712, 272504992, 980656768, 3529064512, 12699954496, 45703002496, 164470230016, 591874824064, 2129964841216, 7665050176768, 27584020672768 (list; graph; refs; listen; history; text; internal format)
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

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Last modified September 24 03:26 EDT 2021. Contains 347623 sequences. (Running on oeis4.)