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

Terms

a(0) =1a(1) =0a(2) =3a(3) =2a(4) =9a(5) =12a(6) =31a(7) =54a(8) =117a(9) =224a(10) =459a(11) =906a(12) =1825a(13) =3636a(14) =7287a(15) =14558a(16) =29133a(17) =58248a(18) =116515a(19) =233010a(20) =466041a(21) =932060a(22) =1864143a(23) =3728262a(24) =7456549a(25) =14913072a(26) =29826171a(27) =59652314a(28) =119304657a(29) =238609284