a(n) = 3^n - n^4.

Terms

a(0) =1a(1) =2a(2) =-7a(3) =-54a(4) =-175a(5) =-382a(6) =-567a(7) =-214a(8) =2465a(9) =13122a(10) =49049a(11) =162506a(12) =510705a(13) =1565762a(14) =4744553a(15) =14298282a(16) =42981185a(17) =129056642a(18) =387315513a(19) =1162131146a(20) =3486624401a(21) =10460158722a(22) =31380825353a(23) =94142898986a(24) =282429204705a(25) =847288218818