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

0,3

Comments

There is no constraint on touching any particular sector.

Links

Table of n, a(n) for n=0..7.

Crossrefs

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

Sequence in context: A244666 A101531 A099607 * A301809 A056780 A324614

Adjacent sequences: A077547 A077548 A077549 * A077551 A077552 A077553

Keyword

nonn

Author

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

Status

approved