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

Terms

a(0) =-1a(1) =-1a(2) =1a(3) =-4a(4) =8a(5) =-19a(6) =42a(7) =-95a(8) =213a(9) =-479a(10) =1076a(11) =-2418a(12) =5433a(13) =-12208a(14) =27431a(15) =-61637a(16) =138497a(17) =-311200a(18) =699260a(19) =-1571223a(20) =3530506a(21) =-7932975a(22) =17825233a(23) =-40052935a(24) =89998128a(25) =-202223958a(26) =454393109a(27) =-1021012048a(28) =2294193247a(29) =-5155005433