Number of lattice paths from (0,0) to (n,n) consisting of steps U=(1,1), H=(1,0) and S=(0,1) such that the first step leaving the diagonal (if any) is an H step and the last step joining the diagonal (if any) is a S step.

A226995

Number of lattice paths from (0,0) to (n,n) consisting of steps U=(1,1), H=(1,0) and S=(0,1) such that the first step leaving the diagonal (if any) is an H step and the last step joining the diagonal (if any) is a S step.

Terms

    a(0) =1a(1) =2a(2) =6a(3) =23a(4) =103a(5) =504a(6) =2588a(7) =13661a(8) =73373a(9) =398814a(10) =2186818a(11) =12072275a(12) =67004451a(13) =373532596a(14) =2089994360a(15) =11730304377a(16) =66012996217a(17) =372350924666

External references