Running sum of every third term in the {+1,-1}-version of Thue-Morse sequence A010060.

Terms

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