A024639 n written in fractional base 7/2.

0, 1, 2, 3, 4, 5, 6, 20, 21, 22, 23, 24, 25, 26, 40, 41, 42, 43, 44, 45, 46, 60, 61, 62, 63, 64, 65, 66, 210, 211, 212, 213, 214, 215, 216, 230, 231, 232, 233, 234, 235, 236, 250, 251, 252, 253, 254, 255, 256, 400, 401, 402, 403, 404, 405, 406, 420, 421, 422, 423, 424, 425