a(n) = (9/5)*(1+4*(-9)^(n-1)).

Terms

a(0) =1a(1) =9a(2) =-63a(3) =585a(4) =-5247a(5) =47241a(6) =-425151a(7) =3826377a(8) =-34437375a(9) =309936393a(10) =-2789427519a(11) =25104847689a(12) =-225943629183