a(n) = (7*n+2)^6.

Terms

a(0) =64a(1) =531441a(2) =16777216a(3) =148035889a(4) =729000000a(5) =2565726409a(6) =7256313856a(7) =17596287801a(8) =38068692544a(9) =75418890625a(10) =139314069504a(11) =243087455521a(12) =404567235136a(13) =646990183449a(14) =1000000000000