a(n) = 3^n - n^11.

Terms

a(0) =1a(1) =2a(2) =-2039a(3) =-177120a(4) =-4194223a(5) =-48827882a(6) =-362796327a(7) =-1977324556a(8) =-8589928031a(9) =-31381039926a(10) =-99999940951a(11) =-285311493464a(12) =-743007839247