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

 Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 59th year, we have over 358,000 sequences, and we’ve crossed 10,300 citations (which often say “discovered thanks to the OEIS”). Other ways to Give
 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 R. H. Hardin, Table of n, a(n) for n = 1..210 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 Adjacent sequences: A220673 A220674 A220675 * A220677 A220678 A220679 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.

Last modified November 27 11:32 EST 2022. Contains 358403 sequences. (Running on oeis4.)