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

Terms

a(0) =1a(1) =0a(2) =2a(3) =6a(4) =1a(5) =9a(6) =23a(7) =2a(8) =34a(9) =88a(10) =9a(11) =131a(12) =339a(13) =34a(14) =504a(15) =1304a(16) =131a(17) =1939a(18) =5017a(19) =504a(20) =7460a(21) =19302a(22) =1939a(23) =28701a(24) =74261a(25) =7460a(26) =110422a(27) =285706a(28) =28701a(29) =424829