A143825 This sequence displays every positive integer exactly three times; there is one number between the first and second 1's and one number between the second and third 1's; two numbers between the first and second 2's and two numbers between the second and third 2's; ... n numbers between the first and second n's and n numbers between the second and third n's.

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