a(0)=2. a(n+1) = 2*a(n) + period 4: repeat -5,1,3,1.

Terms

a(0) =2a(1) =-1a(2) =-1a(3) =1a(4) =3a(5) =1a(6) =3a(7) =9a(8) =19a(9) =33a(10) =67a(11) =137a(12) =275a(13) =545a(14) =1091a(15) =2185a(16) =4371a(17) =8737a(18) =17475a(19) =34953a(20) =69907a(21) =139809a(22) =279619a(23) =559241a(24) =1118483a(25) =2236961a(26) =4473923a(27) =8947849a(28) =17895699a(29) =35791393