a(n) = (2*n+1)^8.

Terms

a(0) =1a(1) =6561a(2) =390625a(3) =5764801a(4) =43046721a(5) =214358881a(6) =815730721a(7) =2562890625a(8) =6975757441a(9) =16983563041a(10) =37822859361a(11) =78310985281a(12) =152587890625a(13) =282429536481a(14) =500246412961a(15) =852891037441