

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
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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.


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CROSSREFS



KEYWORD

nonn,more,nice,walk


AUTHOR



EXTENSIONS



STATUS

approved



