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

Terms

a(0) =0a(1) =1a(2) =-3a(3) =5a(4) =-12a(5) =25a(6) =-54a(7) =116a(8) =-249a(9) =535a(10) =-1149a(11) =2468a(12) =-5301a(13) =11386a(14) =-24456a(15) =52529a(16) =-112827a(17) =242341a(18) =-520524a(19) =1118033a(20) =-2401422a(21) =5158012a(22) =-11078889a(23) =23796335a(24) =-51112125a(25) =109783684a(26) =-235804269a(27) =506483762a(28) =-1087875984a(29) =2336647777