a(n) = (8*n + 2)^6.

Terms

a(0) =64a(1) =1000000a(2) =34012224a(3) =308915776a(4) =1544804416a(5) =5489031744a(6) =15625000000a(7) =38068692544a(8) =82653950016a(9) =164206490176a(10) =304006671424a(11) =531441000000a(12) =885842380864