Number of skew Dyck paths of semilength n having no DD's.

Terms

a(0) =1a(1) =1a(2) =2a(3) =5a(4) =14a(5) =41a(6) =124a(7) =386a(8) =1230a(9) =3992a(10) =13150a(11) =43856a(12) =147796a(13) =502530a(14) =1721856a(15) =5939353a(16) =20608102a(17) =71879003a(18) =251876040a(19) =886309559a(20) =3130552258a(21) =11095355269a(22) =39447022648a(23) =140645181280a(24) =502773092420