a(n) = (2n + 1)*5^n.

Terms

a(0) =1a(1) =15a(2) =125a(3) =875a(4) =5625a(5) =34375a(6) =203125a(7) =1171875a(8) =6640625a(9) =37109375a(10) =205078125a(11) =1123046875a(12) =6103515625a(13) =32958984375a(14) =177001953125a(15) =946044921875