a(n) = 3^n - n^8.

Terms

a(0) =1a(1) =2a(2) =-247a(3) =-6534a(4) =-65455a(5) =-390382a(6) =-1678887a(7) =-5762614a(8) =-16770655a(9) =-43027038a(10) =-99940951a(11) =-214181734a(12) =-429450255a(13) =-814136398a(14) =-1471006087a(15) =-2548541718a(16) =-4251920575a(17) =-6846617278a(18) =-10632540087a(19) =-15821301574a(20) =-22113215599