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%I #12 Aug 01 2012 12:31:57
%S 2,2,6,10,32,62,210,436,1540,3346,12192,27344,102054,234388,891574,
%T 2085940,8057844,19134786,74864648,179968564,711708544
%N Meandric numbers for a river crossing two perpendicular roads at n points, beginning in the (-,-) quadrant and ending in any quadrant.
%C a(n) = number of ways that a directed curve (or arrow) can start in the (-,-) quadrant, cross the x and y axes at exactly n points and end in any quadrant.
%F a(2n+1) = 2*A076906(2n+1).
%Y Cf. A005316, A076876, A076906, A076875 (undirected case).
%Y Cf. A077551 (cross x axis first).
%K nonn,more
%O 0,1
%A _N. J. A. Sloane_ and _Jon Wild_, Nov 26 2002
%E a(6) and a(7) corrected Aug 25 2003
%E a(7) corrected by _Robert Price_, Jul 29 2012
%E a(8)-a(20) from _Robert Price_, Aug 01 2012