Number of paths from (0,0) to (3n,0) that stay in first quadrant (but may touch horizontal axis), where each step is (2,1),(1,2) or (1,-1) and start with (1,2).

A033296

Number of paths from (0,0) to (3n,0) that stay in first quadrant (but may touch horizontal axis), where each step is (2,1),(1,2) or (1,-1) and start with (1,2).

Terms

    a(0) =1a(1) =1a(2) =6a(3) =42a(4) =326a(5) =2706a(6) =23526a(7) =211546a(8) =1951494a(9) =18366882a(10) =175674054a(11) =1702686090a(12) =16686795846a(13) =165079509042

External references