a(n) = 3^n - n^6.

Terms

a(0) =1a(1) =2a(2) =-55a(3) =-702a(4) =-4015a(5) =-15382a(6) =-45927a(7) =-115462a(8) =-255583a(9) =-511758a(10) =-940951a(11) =-1594414a(12) =-2454543a(13) =-3232486a(14) =-2746567a(15) =2958282a(16) =26269505a(17) =105002594a(18) =353408265a(19) =1115215586a(20) =3422784401a(21) =10374587082a(22) =31267679705a(23) =93995142938a(24) =282238433505a(25) =847044468818