Number of Dyck paths of semilength n having no UUDD's starting at level 0.

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =10a(5) =31a(6) =98a(7) =321a(8) =1078a(9) =3686a(10) =12789a(11) =44919a(12) =159407a(13) =570704a(14) =2058817a(15) =7476621a(16) =27310345a(17) =100275628a(18) =369886451a(19) =1370066394a(20) =5093778398a(21) =19002602171a(22) =71109895075a(23) =266855940177