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A077550
Number of nonisomorphic ways a river (or undirected line) can cross two perpendicular roads n times (orbits of A076875 under symmetry group of order 8).
1
1, 1, 2, 3, 9, 21, 54, 131
OFFSET
0,3
COMMENTS
There is no constraint on touching any particular sector.
CROSSREFS
Cf. A076875 (total number of solutions), A076906, A076907 (if line is directed)
Sequence in context: A244666 A101531 A099607 * A301809 A056780 A324614
KEYWORD
nonn
AUTHOR
N. J. A. Sloane and Jon Wild, Aug 25 2003
STATUS
approved