Expansion of g.f. (1 - 2*x)/(1 - 5*x).

Terms

a(0) =1a(1) =3a(2) =15a(3) =75a(4) =375a(5) =1875a(6) =9375a(7) =46875a(8) =234375a(9) =1171875a(10) =5859375a(11) =29296875a(12) =146484375a(13) =732421875a(14) =3662109375a(15) =18310546875a(16) =91552734375a(17) =457763671875