A037893 a(n)=(1/2)*Sum{|d(i)-e(i)|} where Sum{d(i)*7^i} is the base 7 representation of n and e(i) are the digits d(i) in reverse order.

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