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

Terms

a(0) =0a(1) =0a(2) =50a(3) =750a(4) =7500a(5) =62500a(6) =468750a(7) =3281250a(8) =21875000a(9) =140625000a(10) =878906250a(11) =5371093750a(12) =32226562500a(13) =190429687500