A077551 Meandric numbers for a river (or directed line) crossing two perpendicular roads at n points, beginning in the (-,-) quadrant, crossing x axis first and ending in any quadrant.
0, 1, 3, 5, 16, 31, 105, 218, 770, 1673, 6096, 13672, 51027, 117194, 445787, 1042970, 4028922, 9567393, 37432324, 89984282, 355854272
Offset: 0
Crossrefs
Similar to A076907 but must cross x axis first.
Extensions
a(7) corrected by Robert Price, Jul 29 2012
a(8)-a(20) from Robert Price, Aug 14 2012