a(n) = (3*n+1)^8.

Terms

a(0) =1a(1) =65536a(2) =5764801a(3) =100000000a(4) =815730721a(5) =4294967296a(6) =16983563041a(7) =54875873536a(8) =152587890625a(9) =377801998336a(10) =852891037441