Sum C(n-3k,3k+1), k=0..floor(n/6).

Terms

a(0) =0a(1) =1a(2) =2a(3) =3a(4) =4a(5) =5a(6) =6a(7) =8a(8) =13a(9) =24a(10) =45a(11) =81a(12) =138a(13) =224a(14) =352a(15) =546a(16) =851a(17) =1348a(18) =2175a(19) =3556a(20) =5843a(21) =9582a(22) =15624a(23) =25317a(24) =40836a(25) =65737a(26) =105863a(27) =170796a(28) =276160a(29) =447272