a(n) = 5^n*(n^2 - n + 50)/50.

Terms

a(0) =1a(1) =5a(2) =26a(3) =140a(4) =775a(5) =4375a(6) =25000a(7) =143750a(8) =828125a(9) =4765625a(10) =27343750a(11) =156250000a(12) =888671875a(13) =5029296875a(14) =28320312500a(15) =158691406250a(16) =885009765625