Smallest power (>=2) >= n!.

Terms

a(0) =1a(1) =4a(2) =8a(3) =25a(4) =121a(5) =729a(6) =5041a(7) =40401a(8) =363609a(9) =3629025a(10) =39917124a(11) =479040769a(12) =6227103744a(13) =87178467600