a(n+3) = 6*a(n) - 5*a(n+2), a(0) = -1, a(1) = 3, a(2) = -15.

Terms

a(0) =-1a(1) =3a(2) =-15a(3) =69a(4) =-327a(5) =1545a(6) =-7311a(7) =34593a(8) =-163695a(9) =774609a(10) =-3665487a(11) =17345265a(12) =-82078671a(13) =388400433a(14) =-1837930575a(15) =8697180849a(16) =-41155501647a(17) =194749924785a(18) =-921566538831