a(n) = (8*n + 1)^6.

Terms

a(0) =1a(1) =531441a(2) =24137569a(3) =244140625a(4) =1291467969a(5) =4750104241a(6) =13841287201a(7) =34296447249a(8) =75418890625a(9) =151334226289a(10) =282429536481a(11) =496981290961a(12) =832972004929