a(n) = (6*n + 5)^6.

Terms

a(0) =15625a(1) =1771561a(2) =24137569a(3) =148035889a(4) =594823321a(5) =1838265625a(6) =4750104241a(7) =10779215329a(8) =22164361129a(9) =42180533641a(10) =75418890625a(11) =128100283921a(12) =208422380089a(13) =326940373369a(14) =496981290961a(15) =735091890625