a(n) = A000217(A000041(n)).

Terms

a(0) =1a(1) =1a(2) =3a(3) =6a(4) =15a(5) =28a(6) =66a(7) =120a(8) =253a(9) =465a(10) =903a(11) =1596a(12) =3003a(13) =5151a(14) =9180a(15) =15576a(16) =26796a(17) =44253a(18) =74305a(19) =120295a(20) =196878a(21) =314028a(22) =502503a(23) =788140a(24) =1241100a(25) =1917861a(26) =2968266a(27) =4531555a(28) =6913621a(29) =10421895