Largest power (>=2) <= n!.

Terms

a(0) =1a(1) =1a(2) =4a(3) =16a(4) =100a(5) =676a(6) =4913a(7) =40000a(8) =362404a(9) =3625216a(10) =39904489a(11) =478996996a(12) =6226945921a(13) =87177877081