Generalized nim sum n + n in base 10.

Terms

a(0) =0a(1) =2a(2) =4a(3) =6a(4) =8a(5) =0a(6) =2a(7) =4a(8) =6a(9) =8a(10) =20a(11) =22a(12) =24a(13) =26a(14) =28a(15) =20a(16) =22a(17) =24a(18) =26a(19) =28a(20) =40a(21) =42a(22) =44a(23) =46a(24) =48a(25) =40a(26) =42a(27) =44a(28) =46a(29) =48