a(n) = 8^n - n^3.

Terms

a(0) =1a(1) =7a(2) =56a(3) =485a(4) =4032a(5) =32643a(6) =261928a(7) =2096809a(8) =16776704a(9) =134216999a(10) =1073740824a(11) =8589933261a(12) =68719475008a(13) =549755811691