Number of equivalence classes of ballot paths of length n for the string ddu.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =3a(6) =4a(7) =5a(8) =8a(9) =12a(10) =17a(11) =23a(12) =35a(13) =52a(14) =75a(15) =105a(16) =157a(17) =232a(18) =337a(19) =480a(20) =712a(21) =1049a(22) =1529a(23) =2199a(24) =3248a(25) =4777a(26) =6976a(27) =10092a(28) =14869a(29) =21845