a(n) = (4 + (-9)^n)/5.

Terms

a(0) =1a(1) =-1a(2) =17a(3) =-145a(4) =1313a(5) =-11809a(6) =106289a(7) =-956593a(8) =8609345a(9) =-77484097a(10) =697356881a(11) =-6276211921a(12) =56485907297a(13) =-508373165665