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A086031 Number of nonisomorphic ways a loop can cross two parallel roads 2n times. 2
1, 1, 3, 7, 37, 207, 1470, 11169, 91166, 776841, 6865598, 62443973 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

There is no obligation to cross the lower road (cf. A077054).

LINKS

Table of n, a(n) for n=0..11.

CROSSREFS

Cf. A077054. Isomorphism classes from A085973.

Sequence in context: A087208 A161675 A208809 * A174734 A152560 A162926

Adjacent sequences:  A086028 A086029 A086030 * A086032 A086033 A086034

KEYWORD

nonn

AUTHOR

N. J. A. Sloane and Jon Wild, Aug 25 2003

STATUS

approved

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Last modified August 25 09:58 EDT 2019. Contains 326324 sequences. (Running on oeis4.)