a(n) = binomial(n+7, 7)*5^n.

Terms

a(0) =1a(1) =40a(2) =900a(3) =15000a(4) =206250a(5) =2475000a(6) =26812500a(7) =268125000a(8) =2513671875a(9) =22343750000a(10) =189921875000