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

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =3a(5) =5a(6) =6a(7) =9a(8) =9a(9) =12a(10) =9a(11) =9a(12) =0a(13) =-9a(14) =-27a(15) =-54a(16) =-81a(17) =-135a(18) =-162a(19) =-243a(20) =-243a(21) =-324a(22) =-243a(23) =-243a(24) =0a(25) =243a(26) =729a(27) =1458a(28) =2187a(29) =3645