A031482 n-th number k which in base 7 has the same number of 0's as 6's.

1, 2, 3, 4, 5, 8, 9, 10, 11, 12, 15, 16, 17, 18, 19, 22, 23, 24, 25, 26, 29, 30, 31, 32, 33, 36, 37, 38, 39, 40, 42, 55, 57, 58, 59, 60, 61, 64, 65, 66, 67, 68, 71, 72, 73, 74, 75, 78, 79, 80, 81, 82, 85, 86, 87, 88, 89, 91, 104, 106, 107, 108