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, 2, 3, 9, 21, 54, 131

Offset: 0

Author

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

Keywords

• nonn

Comments

There is no constraint on touching any particular sector.

Crossrefs

Cf. A076875 (total number of solutions), A076906, A076907 (if line is directed)