a(0)=1, a(1)=1; thereafter a(n) = -a(n-1) - 2*a(n-2).

Terms

a(0) =1a(1) =1a(2) =-3a(3) =1a(4) =5a(5) =-7a(6) =-3a(7) =17a(8) =-11a(9) =-23a(10) =45a(11) =1a(12) =-91a(13) =89a(14) =93a(15) =-271a(16) =85a(17) =457a(18) =-627a(19) =-287a(20) =1541a(21) =-967a(22) =-2115a(23) =4049a(24) =181a(25) =-8279a(26) =7917a(27) =8641a(28) =-24475a(29) =7193