a(n) = 3*a(n-1) + 4*a(n-2) + a(n-3), a(0) = 1, a(1) = -1, a(2) = -1 .

Terms

a(0) =1a(1) =-1a(2) =-1a(3) =-6a(4) =-23a(5) =-94a(6) =-380a(7) =-1539a(8) =-6231a(9) =-25229a(10) =-102150a(11) =-413597a(12) =-1674620a(13) =-6780398a(14) =-27453271a(15) =-111156025a(16) =-450061557a(17) =-1822262042a(18) =-7378188379a(19) =-29873674862a(20) =-120956040144a(21) =-489741008259