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

Terms

a(0) =0a(1) =262144a(2) =16777216a(3) =191102976a(4) =1073741824a(5) =4096000000a(6) =12230590464a(7) =30840979456a(8) =68719476736a(9) =139314069504a(10) =262144000000a(11) =464404086784a(12) =782757789696