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A086031
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Number of nonisomorphic ways a loop can cross two parallel roads 2n times.
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2
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1, 1, 3, 7, 37, 207, 1470, 11169, 91166, 776841, 6865598, 62443973
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OFFSET
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0,3
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COMMENTS
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There is no obligation to cross the lower road (cf. A077054).
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LINKS
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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