a(n) = Sum_{d|n} phi(d)*8^(n/d).

Terms

a(0) =0a(1) =8a(2) =72a(3) =528a(4) =4176a(5) =32800a(6) =262800a(7) =2097200a(8) =16781472a(9) =134218800a(10) =1073774880a(11) =8589934672a(12) =68719748256a(13) =549755813984