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

Terms

a(0) =1a(1) =6a(2) =21a(3) =81a(4) =306a(5) =1161a(6) =4401a(7) =16686a(8) =63261a(9) =239841a(10) =909306a(11) =3447441a(12) =13070241a(13) =49553046a(14) =187869861a(15) =712268721a(16) =2700415746a(17) =10238053401a(18) =38815407441a(19) =147160382526a(20) =557927369901