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

Terms

a(0) =0a(1) =3a(2) =0a(3) =9a(4) =-3a(5) =27a(6) =-18a(7) =84a(8) =-81a(9) =270a(10) =-327a(11) =891a(12) =-1251a(13) =3000a(14) =-4644a(15) =10251a(16) =-16932a(17) =35397a(18) =-61047a(19) =123123a(20) =-218538a(21) =430416a(22) =-778737a(23) =1509786a(24) =-2766627a(25) =5308095a(26) =-9809667a(27) =18690912a(28) =-34737096a(29) =65882403