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

Terms

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