a(n) = 2(a(n-2) - a(n-1)) + a(n-3) where a(0)=-3, a(1)=11 & a(2)=-30.

Terms

a(0) =-3a(1) =11a(2) =-30a(3) =79a(4) =-207a(5) =542a(6) =-1419a(7) =3715a(8) =-9726a(9) =25463a(10) =-66663a(11) =174526a(12) =-456915a(13) =1196219a(14) =-3131742a(15) =8199007a(16) =-21465279a(17) =56196830a(18) =-147125211a(19) =385178803a(20) =-1008411198a(21) =2640054791a(22) =-6911753175a(23) =18095204734a(24) =-47373861027a(25) =124026378347a(26) =-324705274014a(27) =850089443695