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!)
A221521 Number of 0..5 arrays of length n with each element differing from at least one neighbor by 2 or more. 1
0, 20, 68, 400, 1940, 9982, 50400, 256018, 1297924, 6584320, 33394958, 169387004, 859152000, 4357755890, 22103183110, 112110699524, 568642349004, 2884239836106, 14629299498936, 74202014273586, 376363810775194 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Column 5 of A221524.

LINKS

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

FORMULA

Empirical: a(n) = 2*a(n-1) +11*a(n-2) +20*a(n-3) +17*a(n-4) -3*a(n-5) +a(n-6).

Empirical g.f.: 2*x^2*(10 + 14*x + 22*x^2 - 4*x^3 + x^4) / (1 - 2*x - 11*x^2 - 20*x^3 - 17*x^4 + 3*x^5 - x^6). - Colin Barker, Oct 18 2017

EXAMPLE

Some solutions for n=6

..2....4....0....4....2....0....0....5....2....1....2....0....0....0....4....5

..5....2....5....0....5....5....3....2....5....4....4....4....5....5....0....0

..2....1....2....1....0....1....1....0....1....1....0....3....0....1....0....3

..3....4....4....4....4....5....4....2....3....1....2....5....1....3....2....5

..1....5....4....5....1....1....0....3....1....5....1....5....3....5....1....3

..4....3....0....1....3....3....2....0....3....3....5....0....5....0....3....1

CROSSREFS

Sequence in context: A158444 A235281 A303620 * A145191 A044158 A044539

Adjacent sequences:  A221518 A221519 A221520 * A221522 A221523 A221524

KEYWORD

nonn

AUTHOR

R. H. Hardin, Jan 19 2013

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 October 1 17:45 EDT 2020. Contains 337444 sequences. (Running on oeis4.)