a(n) = (number of digits <=4)-(number of digits >4) in base 10 representation of n.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =-1a(5) =-1a(6) =-1a(7) =-1a(8) =-1a(9) =2a(10) =2a(11) =2a(12) =2a(13) =2a(14) =0a(15) =0a(16) =0a(17) =0a(18) =0a(19) =2a(20) =2a(21) =2a(22) =2a(23) =2a(24) =0a(25) =0a(26) =0a(27) =0a(28) =0a(29) =2