%I A077550
%S A077550 1,1,2,3,9,21,54,131
%N 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).
%C A077550 There is no constraint on touching any particular sector.
%Y A077550 Cf. A076875 (total number of solutions), A076906, A076907 (if line is 
               directed)
%Y A077550 Sequence in context: A015951 A101531 A099607 this_sequence A056780 A141505 
               A111360
%Y A077550 Adjacent sequences: A077547 A077548 A077549 this_sequence A077551 A077552 
               A077553
%K A077550 nonn
%O A077550 0,3
%A A077550 N. J. A. Sloane (njas(AT)research.att.com) and Jon Wild (wild(AT)music.mcgill.ca), 
               Aug 25 2003