A026338 a(n) = a(m) if a(m) has already occurred exactly once and n = m+[ m/2 ]+1, else a(n) = least positive integer that has not yet occurred.

1, 1, 2, 3, 2, 4, 3, 5, 6, 4, 7, 8, 5, 6, 9, 10, 7, 11, 8, 12, 13, 14, 9, 15, 10, 16, 17, 11, 18, 19, 12, 13, 20, 14, 21, 22, 15, 23, 24, 16, 17, 25, 26, 18, 27, 19, 28, 29, 30, 20, 31, 32, 21, 33, 22, 34, 35, 23, 24, 36, 37, 38, 39, 25, 26, 40