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!)
A199697 Number of -1..1 arrays x(0..n-1) of n elements with zero sum and no two neighbors equal. 3
1, 2, 6, 8, 14, 32, 56, 100, 204, 388, 722, 1416, 2750, 5256, 10222, 19944, 38650, 75272, 147142, 287120, 561018, 1098752, 2152092, 4217620, 8276376, 16250292, 31921374, 62754072, 123440514, 242921784, 478310952, 942260548, 1856994908, 3661288036 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
Column 1 of A199704
LINKS
FORMULA
G.f.: ((x+1)^2*sqrt((1-x)/(1-x-4*x^3))-2*x-1)/x. - Stefan Hollos, Mar 08 2017
EXAMPLE
All solutions for n=5
..0...-1....1...-1....1...-1...-1....0....1...-1....0....1....1....0
.-1....1...-1....1....0....1....0...-1...-1....1....1...-1...-1....1
..1....0....0...-1...-1...-1....1....0....1....0....0....1....0...-1
.-1...-1....1....1....1....0...-1....1....0....1...-1...-1...-1....1
..1....1...-1....0...-1....1....1....0...-1...-1....0....0....1...-1
MATHEMATICA
Rest@ CoefficientList[Series[((x + 1)^2*Sqrt[(1 - x)/(1 - x - 4*x^3)] - 2 x - 1)/x, {x, 0, 34}], x] (* Michael De Vlieger, Mar 08 2017 *)
CROSSREFS
Sequence in context: A107019 A269831 A048133 * A339976 A135619 A067795
KEYWORD
nonn
AUTHOR
R. H. Hardin, Nov 09 2011
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 March 28 14:38 EDT 2024. Contains 371254 sequences. (Running on oeis4.)