login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A268768 Number of n X 2 0..2 arrays with some element plus some horizontally, vertically, diagonally or antidiagonally adjacent neighbor totalling two exactly once. 1
3, 12, 32, 100, 248, 620, 1456, 3380, 7656, 17148, 37920, 83140, 180824, 390796, 839824, 1796180, 3825352, 8116764, 17165568, 36195300, 76118840, 159694252, 334301552, 698429300, 1456510888, 3032326460, 6303262176, 13083742980 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

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

FORMULA

Empirical: a(n) = 2*a(n-1) + 3*a(n-2) - 4*a(n-3) - 4*a(n-4) for n>5.

Conjectures from Colin Barker, Jan 14 2019: (Start)

G.f.: x*(3 + 6*x - x^2 + 12*x^3 + 12*x^4) / ((1 + x)^2*(1 - 2*x)^2).

a(n) = (4/27)*(7*((-1)^n-2^n) + 3*((-1)^n + 2^(2+n))*n) for n>1.

(End)

EXAMPLE

Some solutions for n=4:

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

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

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

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

CROSSREFS

Column 2 of A268774.

Sequence in context: A037236 A309693 A288605 * A174963 A054602 A083725

Adjacent sequences:  A268765 A268766 A268767 * A268769 A268770 A268771

KEYWORD

nonn

AUTHOR

R. H. Hardin, Feb 13 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 | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified January 29 01:46 EST 2020. Contains 331328 sequences. (Running on oeis4.)