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A000644
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Number of loops of length 4n on square grid that turn at each step and return to start in original direction.
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1
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1, 1, 3, 7, 31, 138, 808, 4956, 33047, 227328, 1614793, 11710299, 86495618, 648399937, 4923728056
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OFFSET
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1,3
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COMMENTS
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Loops cannot overlap and rotations and reflections of a given loop are not counted. - Sean A. Irvine, Oct 18 2015
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REFERENCES
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D. E. Knuth, The Texbook, p. 390.
D. E. Knuth, personal communication.
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LINKS
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CROSSREFS
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KEYWORD
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nonn,more,nice,walk
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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