a(n) = 3^n - n^5.

Terms

a(0) =1a(1) =2a(2) =-23a(3) =-216a(4) =-943a(5) =-2882a(6) =-7047a(7) =-14620a(8) =-26207a(9) =-39366a(10) =-40951a(11) =16096a(12) =282609a(13) =1223030a(14) =4245145a(15) =13589532a(16) =41998145a(17) =127720306a(18) =385530921a(19) =1159785368a(20) =3483584401