Expansion of g.f. (1-2*x)/(1-9*x).

Terms

a(0) =1a(1) =7a(2) =63a(3) =567a(4) =5103a(5) =45927a(6) =413343a(7) =3720087a(8) =33480783a(9) =301327047a(10) =2711943423a(11) =24407490807a(12) =219667417263