Expansion of (1-x)/(1-x-3x^3).

Terms

a(0) =1a(1) =0a(2) =0a(3) =3a(4) =3a(5) =3a(6) =12a(7) =21a(8) =30a(9) =66a(10) =129a(11) =219a(12) =417a(13) =804a(14) =1461a(15) =2712a(16) =5124a(17) =9507a(18) =17643a(19) =33015a(20) =61536a(21) =114465a(22) =213510a(23) =398118a(24) =741513a(25) =1382043a(26) =2576397a(27) =4800936a(28) =8947065a(29) =16676256