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!)
A000644 Number of loops of length 4n on square grid that turn at each step and return to start in original direction. 1
1, 1, 3, 7, 31, 138, 808, 4956, 33047, 227328, 1614793, 11710299, 86495618, 648399937, 4923728056 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
COMMENTS
Loops cannot overlap and rotations and reflections of a given loop are not counted. - Sean A. Irvine, Oct 18 2015
REFERENCES
D. E. Knuth, The Texbook, p. 390.
D. E. Knuth, personal communication.
LINKS
Douglas A. Torrance, Enumeration of planar Tangles, arXiv:1906.01541 [math.CO], 2019.
CROSSREFS
Sequence in context: A123488 A121620 A042271 * A015459 A115083 A141385
KEYWORD
nonn,more,nice,walk
AUTHOR
EXTENSIONS
a(11) from Sean A. Irvine, Oct 18 2015
Offset corrected and a(12)-a(15) from Bert Dobbelaere, Jan 11 2020
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 2 05:08 EST 2024. Contains 370460 sequences. (Running on oeis4.)