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

A027307

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

Terms

    a(0) =1a(1) =2a(2) =10a(3) =66a(4) =498a(5) =4066a(6) =34970a(7) =312066a(8) =2862562a(9) =26824386a(10) =255680170a(11) =2471150402a(12) =24161357010a(13) =238552980386

External references