Replace 4^k with (-4)^k in base 4 expansion of n.

Terms

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