login
This site is supported by donations to The OEIS Foundation.

 

Logo

Invitation: celebrating 50 years of OEIS, 250000 sequences, and Sloane's 75th, there will be a conference at DIMACS, Rutgers, Oct 9-10 2014.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A174469 Number of permutations p of {1,...,n} satisfying p(1)=1 and, if n>1, |p(i)-p((i mod n)+1)| is in {2,3} for i from 1 to n. 1
1, 0, 0, 0, 2, 0, 0, 0, 0, 2, 2, 2, 2, 2, 4, 6, 8, 10, 12, 16, 22, 30, 40, 52, 68, 90, 120, 160, 212, 280, 370, 490, 650, 862, 1142, 1512, 2002, 2652, 3514, 4656, 6168, 8170, 10822, 14336, 18992, 25160, 33330, 44152, 58488, 77480, 102640, 135970 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

COMMENTS

Also the number of directed Hamiltonian cycles in the graph on n vertices {1,...,n}, with i adjacent to j iff 2 <= |i-j| <= 3.

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..1000

Weisstein, Eric W. "Hamiltonian Cycle".

FORMULA

G.f.: (3*x^5-2*x^4+x-1)*x / (x^5+x-1).

a(n) = 2*A017899(n-5) for n>=5.

EXAMPLE

For n = 10 the a(10) = 2 permutations are (1,3,6,9,7,10,8,5,2,4), (1,4,2,5,8,10,7,9,6,3).

MAPLE

a:= n-> `if` (n<2, n, (Matrix (5, (i, j)-> `if` (j-i=1 or i=5 and j in {1, 5}, 1, 0))^n. <<2, -2, (0$3)>>)[1, 1]): seq (a(n), n=1..60);

CROSSREFS

Cf. A017899.

Sequence in context: A028961 A110177 A036273 * A112166 A112167 A230571

Adjacent sequences:  A174466 A174467 A174468 * A174470 A174471 A174472

KEYWORD

nonn

AUTHOR

Alois P. Heinz, Nov 28 2010

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement .

Last modified July 23 14:28 EDT 2014. Contains 244868 sequences.