Semi-meanders: number of ways a semi-infinite directed curve can cross a straight line n times.

A000682

Semi-meanders: number of ways a semi-infinite directed curve can cross a straight line n times.

Terms

    a(0) =1a(1) =1a(2) =2a(3) =4a(4) =10a(5) =24a(6) =66a(7) =174a(8) =504a(9) =1406a(10) =4210a(11) =12198a(12) =37378a(13) =111278a(14) =346846a(15) =1053874a(16) =3328188a(17) =10274466a(18) =32786630a(19) =102511418a(20) =329903058a(21) =1042277722a(22) =3377919260a(23) =10765024432a(24) =35095839848a(25) =112670468128a(26) =369192702554

External references