a(n) = Sum_{k=0..floor(3*n/11)} binomial(3*n-10*k,k).

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =3a(5) =6a(6) =9a(7) =12a(8) =21a(9) =39a(10) =66a(11) =103a(12) =167a(13) =285a(14) =484a(15) =796a(16) =1303a(17) =2167a(18) =3631a(19) =6040a(20) =9988a(21) =16555a(22) =27551a(23) =45838a(24) =76087a(25) =126236a(26) =209685a(27) =348502a(28) =578930a(29) =961269