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

Terms

a(0) =1a(1) =0a(2) =3a(3) =3a(4) =9a(5) =18a(6) =36a(7) =81a(8) =162a(9) =351a(10) =729a(11) =1539a(12) =3240a(13) =6804a(14) =14337a(15) =30132a(16) =63423a(17) =133407a(18) =280665a(19) =590490a(20) =1242216a(21) =2613465a(22) =5498118a(23) =11567043a(24) =24334749a(25) =51195483a(26) =107705376a(27) =226590696a(28) =476702577a(29) =1002888216