a(1)=a(2)=1, a(n+2)=a(n+1)+a(n)+(-2)^n.

Terms

a(0) =1a(1) =1a(2) =0a(3) =5a(4) =-3a(5) =18a(6) =-17a(7) =65a(8) =-80a(9) =241a(10) =-351a(11) =914a(12) =-1485a(13) =3525a(14) =-6152a(15) =13757a(16) =-25163a(17) =54130a(18) =-102105a(19) =214169a(20) =-412224a(21) =850521a(22) =-1658855a(23) =3385970a(24) =-6661493a(25) =13501693a(26) =-26714232a(27) =53896325a(28) =-107035635a(29) =215296146