Partial sums of Berstel sequence (A007420).

Terms

a(0) =0a(1) =0a(2) =1a(3) =3a(4) =3a(5) =-1a(6) =-1a(7) =15a(8) =31a(9) =-1a(10) =-65a(11) =-1a(12) =255a(13) =255a(14) =-513a(15) =-1025a(16) =1023a(17) =4095a(18) =-1a(19) =-12289a(20) =-8193a(21) =32767a(22) =49151a(23) =-65537a(24) =-196609a(25) =65535a(26) =655359a(27) =262143a(28) =-1835009a(29) =-2097153