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A337353
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Number of n-step self-avoiding walks on a square lattice where no step can be in the same direction as the previous step.
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9
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1, 4, 8, 16, 24, 40, 64, 104, 168, 272, 440, 712, 1128, 1808, 2896, 4640, 7368, 11744, 18752, 29920, 47376, 75304, 119824, 190632, 301488, 478160, 759056, 1204848, 1903576, 3014272, 4776504, 7568688, 11947976, 18895760, 29901592, 47317080, 74643504, 117930520, 186413728, 294666160
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OFFSET
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0,2
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LINKS
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FORMULA
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EXAMPLE
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a(5) = 40. The five possible 5-step walks in the first quadrant are:
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+--+ +--+ +--+ +--+
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+--+ +--+ +--+ +--+ +--+
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x--+ x--+ x--+ x--+ x--+ +--+
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Each of these can be taken in eight ways on the square lattice, giving 40 in total.
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CROSSREFS
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KEYWORD
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nonn,walk
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AUTHOR
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STATUS
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approved
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