G.f.: (1+x+x^2+2*x^5-2*x^10)/(1-3*x^3).

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =3a(5) =5a(6) =9a(7) =9a(8) =15a(9) =27a(10) =25a(11) =45a(12) =81a(13) =75a(14) =135a(15) =243a(16) =225a(17) =405a(18) =729a(19) =675a(20) =1215a(21) =2187a(22) =2025a(23) =3645a(24) =6561a(25) =6075a(26) =10935a(27) =19683a(28) =18225a(29) =32805