a(n) = -2*a(n-1) + 4*a(n-2), a(0)=1, a(1)=2.

Terms

a(0) =1a(1) =2a(2) =0a(3) =8a(4) =-16a(5) =64a(6) =-192a(7) =640a(8) =-2048a(9) =6656a(10) =-21504a(11) =69632a(12) =-225280a(13) =729088a(14) =-2359296a(15) =7634944a(16) =-24707072a(17) =79953920a(18) =-258736128a(19) =837287936a(20) =-2709520384a(21) =8768192512a(22) =-28374466560a(23) =91821703168a(24) =-297141272576a(25) =961569357824