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A006817
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Trails of length n on square lattice.
(Formerly M3450)
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1
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1, 4, 12, 36, 108, 316, 916, 2628, 7500, 21268, 60092, 169092, 474924, 1329188, 3715244, 10359636, 28856252, 80220244, 222847804, 618083972, 1713283628, 4742946484, 13123882524, 36274940740, 100226653420, 276669062116
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| A trail is a path which may cross itself but does not reuse an edge. This sequence counts directed paths on the square lattice.
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REFERENCES
| A. J. Guttmann, Lattice trails II: numerical results, J. Phys. A 22 (1989), 575-588.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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CROSSREFS
| Undirected trails-rotation and reflection are counted by A001997.
Sequence in context: A199937 A003212 A156945 * A163315 A003119 A001394
Adjacent sequences: A006814 A006815 A006816 * A006818 A006819 A006820
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KEYWORD
| nonn,walk
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| More terms from David W. Wilson (davidwwilson(AT)comcast.net), Jul 20 2001
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