login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A268905 Number of 2 X n 0..2 arrays with some element plus some horizontally or antidiagonally adjacent neighbor totalling two exactly once. 1
0, 36, 168, 696, 2664, 9720, 34344, 118584, 402408, 1347192, 4461480, 14644152, 47711592, 154472184, 497428776, 1594323000, 5089079016, 16185567096, 51311691432, 162200044728, 511395045480, 1608569870328, 5048863812648 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

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

FORMULA

Empirical: a(n) = 6*a(n-1) - 9*a(n-2) for n>4.

Conjectures from Colin Barker, Jan 16 2019: (Start)

G.f.: 12*x^2*(3 - x)*(1 - x) / (1 - 3*x)^2.

a(n) = 8*3^(n-3) * (8*n-3) for n>2.

(End)

EXAMPLE

Some solutions for n=4:

..0..2..1..2. .2..2..2..1. .0..0..2..1. .1..0..1..0. .1..1..0..1

..2..2..2..2. .1..2..1..0. .0..1..0..0. .1..2..0..0. .0..1..2..2

CROSSREFS

Row 2 of A268904.

Sequence in context: A064500 A264474 A338390 * A017054 A231972 A330770

Adjacent sequences:  A268902 A268903 A268904 * A268906 A268907 A268908

KEYWORD

nonn

AUTHOR

R. H. Hardin, Feb 15 2016

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified September 24 12:33 EDT 2022. Contains 356931 sequences. (Running on oeis4.)