a(n) = (8*n + 7)^6.

Terms

a(0) =117649a(1) =11390625a(2) =148035889a(3) =887503681a(4) =3518743761a(5) =10779215329a(6) =27680640625a(7) =62523502209a(8) =128100283921a(9) =243087455521a(10) =433626201009a(11) =735091890625