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

Terms

a(0) =0a(1) =2a(2) =-1a(3) =3a(4) =-5a(5) =7a(6) =-12a(7) =20a(8) =-31a(9) =51a(10) =-83a(11) =133a(12) =-216a(13) =350a(14) =-565a(15) =915a(16) =-1481a(17) =2395a(18) =-3876a(19) =6272a(20) =-10147a(21) =16419a(22) =-26567a(23) =42985a(24) =-69552a(25) =112538a(26) =-182089a(27) =294627a(28) =-476717a(29) =771343