a(n) = 4^n - n^10.

Terms

a(0) =1a(1) =3a(2) =-1008a(3) =-58985a(4) =-1048320a(5) =-9764601a(6) =-60462080a(7) =-282458865a(8) =-1073676288a(9) =-3486522257a(10) =-9998951424a(11) =-25933230297a(12) =-61900587008a(13) =-137791382985a(14) =-288986219520a(15) =-575576648801