A037901 a(n)=(greatest base 7 digit of n)-(least base 7 digit of n).

0, 0, 0, 0, 0, 0, 1, 0, 1, 2, 3, 4, 5, 2, 1, 0, 1, 2, 3, 4, 3, 2, 1, 0, 1, 2, 3, 4, 3, 2, 1, 0, 1, 2, 5, 4, 3, 2, 1, 0, 1, 6, 5, 4, 3, 2, 1, 0, 1, 1, 2, 3, 4, 5, 6, 1, 0, 1, 2, 3, 4, 5, 2, 1, 1, 2, 3, 4, 5, 3, 2, 2, 2, 3, 4, 5, 4, 3, 3, 3, 3, 4, 5, 5, 4, 4, 4, 4, 4, 5