G.f.: (1-3*x+2*x^2+2*x^4+4*x^5)/((1-x)*(1-3*x-4*x^3)).

Terms

a(0) =1a(1) =1a(2) =3a(3) =13a(4) =45a(5) =153a(6) =517a(7) =1737a(8) =5829a(9) =19561a(10) =65637a(11) =220233a(12) =738949a(13) =2479401a(14) =8319141a(15) =27913225a(16) =93657285a(17) =314248425a(18) =1054398181a(19) =3537823689a(20) =11870464773a(21) =39828987049a(22) =133638255909a(23) =448396626825