a(n) = a(n-3) + 2*a(n-6) + a(n-9).

Terms

a(0) =1a(1) =0a(2) =1a(3) =2a(4) =1a(5) =3a(6) =5a(7) =1a(8) =6a(9) =10a(10) =3a(11) =13a(12) =22a(13) =6a(14) =28a(15) =47a(16) =13a(17) =60a(18) =101a(19) =28a(20) =129a(21) =217a(22) =60a(23) =277a(24) =466a(25) =129a(26) =595a(27) =1001a(28) =277a(29) =1278