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A085973
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Number of ways a loop can cross two parallel roads 2n times.
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1
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3, 2, 5, 22, 123, 800, 5754, 44514, 363893, 3106288, 27457050, 249768040, 2327398572, 22135606604, 214270565106, 2106151496858, 20982672402385, 211545853142240, 2155553788108702, 22174250217880984, 230075164780356214
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OFFSET
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0,1
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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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FORMULA
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MATHEMATICA
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A005315 = Cases[Import["https://oeis.org/A005315/b005315.txt", "Table"], {_, _}][[All, 2]];
A005316 = Cases[Import["https://oeis.org/A005316/b005316.txt", "Table"], {_, _}][[All, 2]];
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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