Generalized nim sum n + n in base 7.

Terms

a(0) =0a(1) =2a(2) =4a(3) =6a(4) =1a(5) =3a(6) =5a(7) =14a(8) =16a(9) =18a(10) =20a(11) =15a(12) =17a(13) =19a(14) =28a(15) =30a(16) =32a(17) =34a(18) =29a(19) =31a(20) =33a(21) =42a(22) =44a(23) =46a(24) =48a(25) =43a(26) =45a(27) =47a(28) =7a(29) =9