Expansion of g.f. (1-3*x)/(1-10*x).

Terms

a(0) =1a(1) =7a(2) =70a(3) =700a(4) =7000a(5) =70000a(6) =700000a(7) =7000000a(8) =70000000a(9) =700000000a(10) =7000000000a(11) =70000000000a(12) =700000000000