a(n) = 3*a(n-3) + a(n-2), a(0)=3, a(1)=0, a(2)=2.

Terms

a(0) =3a(1) =0a(2) =2a(3) =9a(4) =2a(5) =15a(6) =29a(7) =21a(8) =74a(9) =108a(10) =137a(11) =330a(12) =461a(13) =741a(14) =1451a(15) =2124a(16) =3674a(17) =6477a(18) =10046a(19) =17499a(20) =29477a(21) =47637a(22) =81974a(23) =136068a(24) =224885a(25) =381990a(26) =633089a(27) =1056645a(28) =1779059a(29) =2955912