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

Terms

a(0) =0a(1) =0a(2) =1a(3) =0a(4) =1a(5) =2a(6) =5a(7) =8a(8) =17a(9) =34a(10) =69a(11) =136a(12) =273a(13) =546a(14) =1093a(15) =2184a(16) =4369a(17) =8738a(18) =17477a(19) =34952a(20) =69905a(21) =139810a(22) =279621a(23) =559240a(24) =1118481a(25) =2236962a(26) =4473925a(27) =8947848a(28) =17895697a(29) =35791394