a(1)=-1; a(2)=-1; a(3)=-2; a(n) = 4*a(n-1) - 3*a(n-2) for n >= 4.

Terms

a(0) =-1a(1) =-1a(2) =-2a(3) =-5a(4) =-14a(5) =-41a(6) =-122a(7) =-365a(8) =-1094a(9) =-3281a(10) =-9842a(11) =-29525a(12) =-88574a(13) =-265721a(14) =-797162a(15) =-2391485a(16) =-7174454a(17) =-21523361a(18) =-64570082a(19) =-193710245a(20) =-581130734a(21) =-1743392201a(22) =-5230176602a(23) =-15690529805a(24) =-47071589414a(25) =-141214768241a(26) =-423644304722