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

Terms

a(0) =0a(1) =1a(2) =1a(3) =1a(4) =1a(5) =4a(6) =1a(7) =3a(8) =7a(9) =3a(10) =6a(11) =16a(12) =6a(13) =13a(14) =34a(15) =13a(16) =28a(17) =73a(18) =28a(19) =60a(20) =157a(21) =60a(22) =129a(23) =337a(24) =129a(25) =277a(26) =724a(27) =277a(28) =595a(29) =1555