a(n) = n*5^(n-1).

Terms

a(0) =0a(1) =1a(2) =10a(3) =75a(4) =500a(5) =3125a(6) =18750a(7) =109375a(8) =625000a(9) =3515625a(10) =19531250a(11) =107421875a(12) =585937500a(13) =3173828125a(14) =17089843750a(15) =91552734375a(16) =488281250000