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!)
A220676 Number of ways to reciprocally link elements of an n X 3 array either to themselves or to exactly two horizontal, vertical and antidiagonal neighbors, without consecutive collinear links. 1
1, 9, 43, 201, 968, 4604, 22000, 104976, 501096, 2391737, 11415981, 54489429, 260082487, 1241395361, 5925282424, 28281863304, 134991671188, 644326407852, 3075423213984, 14679249263905, 70065270353385, 334427328092001 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
Column 3 of A220681.
LINKS
FORMULA
Empirical: a(n) = 2*a(n-1) + 11*a(n-2) + 10*a(n-3) + 2*a(n-4) + 5*a(n-5) + 4*a(n-6) - a(n-7).
Empirical g.f.: x*(1 + 7*x + 14*x^2 + 6*x^3 + x^4 + 4*x^5 - x^6) / ((1 + x)*(1 - 3*x - 8*x^2 - 2*x^3 - 5*x^5 + x^6)). - Colin Barker, Aug 02 2018
EXAMPLE
Some solutions for n=3 0=self 2=n 3=ne 4=w 6=e 7=sw 8=s (reciprocal directions total 10):
.00.00.00...00.67.48...68.47.00...68.47.00...00.78.00...68.48.00...00.00.00
.00.68.47...38.68.24...23.78.00...23.68.47...38.27.78...26.24.00...68.48.00
.00.23.00...26.24.00...36.24.00...00.23.00...23.36.24...00.00.00...26.24.00
CROSSREFS
Cf. A220681.
Sequence in context: A259181 A330088 A281773 * A110125 A221751 A275793
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 17 2012
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 July 20 12:50 EDT 2024. Contains 374445 sequences. (Running on oeis4.)