a(n) = 3^n - n^9.

Terms

a(0) =1a(1) =2a(2) =-503a(3) =-19656a(4) =-262063a(5) =-1952882a(6) =-10076967a(7) =-40351420a(8) =-134211167a(9) =-387400806a(10) =-999940951a(11) =-2357770544a(12) =-5159248911a(13) =-10602905050a(14) =-20656263815a(15) =-38429010468a(16) =-68676430015a(17) =-118458736334a(18) =-197971869879