Expansion of g.f.: (1 + x)/(1 - 3*x - 2*x^2).

Terms

a(0) =1a(1) =4a(2) =14a(3) =50a(4) =178a(5) =634a(6) =2258a(7) =8042a(8) =28642a(9) =102010a(10) =363314a(11) =1293962a(12) =4608514a(13) =16413466a(14) =58457426a(15) =208199210a(16) =741512482a(17) =2640935866a(18) =9405832562a(19) =33499369418a(20) =119309773378a(21) =424928058970