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

Terms

a(0) =1a(1) =-1a(2) =3a(3) =-7a(4) =17a(5) =-41a(6) =99a(7) =-239a(8) =577a(9) =-1393a(10) =3363a(11) =-8119a(12) =19601a(13) =-47321a(14) =114243a(15) =-275807a(16) =665857a(17) =-1607521a(18) =3880899a(19) =-9369319a(20) =22619537a(21) =-54608393a(22) =131836323a(23) =-318281039a(24) =768398401a(25) =-1855077841a(26) =4478554083a(27) =-10812186007a(28) =26102926097a(29) =-63018038201