0,1

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.

a(2n+1) = 2*A076906(2n+1).

Cf. A005316, A076876, A076906, A076875 (undirected case).

Cf. A077551 (cross x axis first).

Sequence in context: A019310 A014113 A078008 this_sequence A103774 A036052 A091764

Adjacent sequences: A076904 A076905 A076906 this_sequence A076908 A076909 A076910

nonn,more

njas and Jon Wild (wild(AT)music.mcgill.ca), Nov 26 2002

a(6) and a(7) corrected Aug 25 2003